amd64/i386: switch IPI handlers to C code.

Move asm IPIs handlers to C code, so both Xen and native IPI handlers
share the same code.

Reviewed by: jhb
Approved by: gibbs
Sponsored by: Citrix Systems R&D

amd64/amd64/apic_vector.S:
i386/i386/apic_vector.s:
 - Remove asm coded IPI handlers and instead call the newly introduced
   C variants.

amd64/amd64/mp_machdep.c:
i386/i386/mp_machdep.c:
 - Add C coded clones to the asm IPI handlers (moved from
   x86/xen/hvm.c).

i386/include/smp.h:
amd64/include/smp.h:
 - Add prototypes for the C IPI handlers.

x86/xen/hvm.c:
 - Move the C IPI handlers to mp_machdep and call those in the Xen IPI
   handlers.

i386/xen/mp_machdep.c:
 - Add dummy IPI handlers to the i386 Xen PV port (this port doesn't
   support SMP).
xen: add PV/PVH kernel entry point

Add the PV/PVH entry point and the low level functions for PVH
early initialization.

Approved by: gibbs
Sponsored by: Citrix Systems R&D

amd64/amd64/genassym.c:
 - Add __FreeBSD_version define to assym.s so it can be used for the
   Xen notes.

amd64/amd64/locore.S:
 - Make bootstack global so it can be used from Xen kernel entry
   point.

amd64/amd64/xen-locore.S:
 - Add Xen notes to the kernel.
 - Add the Xen PV entry point, that is going to call hammer_time_xen.

amd64/include/asmacros.h:
 - Add ELFNOTE macros.

i386/xen/xen_machdep.c:
 - Define HYPERVISOR_start_info for the XEN i386 PV port, which is
   going to be used in some shared code between PV and PVH.

x86/xen/hvm.c:
 - Define HYPERVISOR_start_info for the PVH port.

x86/xen/pv.c:
 - Introduce hammer_time_xen which is going to perform early setup for
   Xen PVH:
    - Setup shared Xen variables start_info, shared_info and
      xen_store.
    - Set guest type.
    - Create initial page tables as FreeBSD expects to find them.
    - Call into native init function (hammer_time).

xen/xen-os.h:
 - Declare HYPERVISOR_start_info.

conf/files.amd64:
 - Add amd64/amd64/locore.S and x86/xen/pv.c to the list of files.
xen: add macro to detect if running as Dom0

Approved by: gibbs
Sponsored by: Citrix Systems R&D

xen/xen-os.h:
 - Add macro to detect if running as Dom0.
xen: add and enable Xen console for PVH guests

This adds and enables the PV console used on XEN kernels to
GENERIC/XENHVM kernels in order for it to be used on PVH.

Approved by: gibbs
Sponsored by: Citrix Systems R&D

dev/xen/console/console.c:
 - Define console_page.
 - Move xc_printf debug function from i386 XEN code to generic console
   code.
 - Rework xc_printf.
 - Use xen_initial_domain instead of open-coded checks for Dom0.
 - Gate the attach of the PV console to PV(H) guests.

dev/xen/console/xencons_ring.c:
 - Allow the PV Xen console to output earlier by directly signaling
   the event channel in start_info if the event channel is not yet
   initialized.
 - Use HYPERVISOR_start_info instead of xen_start_info.

i386/include/xen/xen-os.h:
 - Remove prototype for xc_printf since it's now declared in global
   xen-os.h

i386/xen/xen_machdep.c:
 - Remove previous version of xc_printf.
 - Remove definition of console_page (now it's defined in the console
   itself).
 - Fix some printf formatting errors.

x86/xen/pv.c:
 - Add some early boot debug messages using xc_printf.
 - Set console_page based on the value passed in start_info.

xen/xen-os.h:
 - Declare console_page and add prototype for xc_printf.
howto_names: unify declaration

Approved by: gibbs
Sponsored by: Citrix Systems R&D

boot/i386/efi/bootinfo.c:
boot/i386/libi386/bootinfo.c:
boot/ia64/common/bootinfo.c:
boot/powerpc/ofw/metadata.c:
boot/powerpc/ps3/metadata.c:
boot/sparc64/loader/metadata.c:
boot/uboot/common/metadata.c:
boot/userboot/userboot/bootinfo.c:
i386/xen/xen_machdep.c:
 - Include sys/boot.h
 - Remove custom definition of howto_names.

sys/boot.h:
 - Define howto_names.

x86/xen/pv.c:
 - Include sys/boot.h
amd64: introduce hook for custom preload metadata parsers

Add hooks to amd64 in order to have diverging implementations, since
on Xen PV the metadata is passed to the kernel in a different form.

Approbed by: gibbs
Sponsored by: Citrix Systems R&D

amd64/amd64/machdep.c:
 - Define init_ops for native.
 - Put native code inside of native_parse_preload_data hook.
 - Call the parse_preload_data in order to fill the metadata info.

x86/include/init.h:
 - Declare the init_ops struct.

x86/xen/pv.c:
 - Declare xen_init_ops that contains the Xen PV implementation of
   init_ops.
 - Implement the parse_preload_data for Xen PVH, the info is fetched
   from HYPERVISOR_start_info->cmd_line as provided by Xen.
xen: rework xen timer so it can be used early in boot process

This should not introduce any functional change, and makes the
functions suitable to be called before we have actually mapped the
vcpu_info struct on a per-cpu basis.

Approved by: gibbs
Sponsored by: Citrix Systems R&D

dev/xen/timer/timer.c:
 - Remove citrical_{enter/exit}, the clock code will already be called
   with preemption disabled when needed. Add a comment to that regard
   in xentimer_get_timecount.
 - Allow xen_fetch_vcpu_time to be called with a specifc vcpu_info
   that will be used to fetch current time.
 - Assert that xentimer_et_start will always be called with preemption
   disabled.
xen: implement an early timer for Xen PVH

When running as a PVH guest, there's no emulated i8254, so we need to
use the Xen PV timer as the early source for DELAY. This change allows
for different implementations of the early DELAY function and
implements a Xen variant for it.

Approved by: gibbs
Sponsored by: Citrix Systems R&D

dev/xen/timer/timer.c:
dev/xen/timer/timer.h:
 - Implement Xen early delay functions using the PV timer and declare
   them.

x86/include/init.h:
 - Add hooks for early clock source initialization and early delay
   functions.

i386/i386/machdep.c:
pc98/pc98/machdep.c:
amd64/amd64/machdep.c:
 - Set early delay hooks to use the i8254 on bare metal.
 - Use clock_init (that will in turn make use of init_ops) to
   initialize the early clock source.

amd64/include/clock.h:
i386/include/clock.h:
 - Declare i8254_delay and clock_init.

i386/xen/clock.c:
 - Rename DELAY to i8254_delay.

x86/isa/clock.c:
 - Introduce clock_init that will take care of initializing the early
   clock by making use of the init_ops hooks.
 - Move non ISA related delay functions to the newly introduced delay
   file.

x86/x86/delay.c:
 - Add moved delay related functions.
 - Implement generic DELAY function that will use the init_ops hooks.

x86/xen/pv.c:
 - Set PVH hooks for the early delay related functions in init_ops.

conf/files.amd64:
conf/files.i386:
conf/files.pc98:
 - Add delay.c to the kernel build.