Implement PV IPIs for PVHVM guests and further converge PV and HVM
IPI implmementations.

Submitted by: Roger Pau Monné
Sponsored by: Citrix Systems R&D
Submitted by: gibbs (misc cleanup, table driven config)
Reviewed by:  gibbs
MFC after: 2 weeks

sys/amd64/include/cpufunc.h:
sys/amd64/amd64/pmap.c:
	Move invltlb_globpcid() into cpufunc.h so that it can be
	used by the Xen HVM version of tlb shootdown IPI handlers.

sys/x86/xen/xen_intr.c:
sys/xen/xen_intr.h:
	Rename xen_intr_bind_ipi() to xen_intr_alloc_and_bind_ipi(),
	and remove the ipi vector parameter.  This api allocates
	an event channel port that can be used for ipi services,
	but knows nothing of the actual ipi for which that port
	will be used.  Removing the unused argument and cleaning
	up the comments surrounding its declaration helps clarify
	its actual role.

sys/amd64/amd64/mp_machdep.c:
sys/amd64/include/cpu.h:
sys/i386/i386/mp_machdep.c:
sys/i386/include/cpu.h:
	Implement a generic framework for amd64 and i386 that allows
	the implementation of certain CPU management functions to
	be selected at runtime.  Currently this is only used for
	the ipi send function, which we optimize for Xen when running
	on a Xen hypervisor, but can easily be expanded to support
	more operations.

sys/x86/xen/hvm.c:
	Implement Xen PV IPI handlers and operations, replacing native
	send IPI.

sys/amd64/include/pcpu.h:
sys/i386/include/pcpu.h:
sys/i386/include/smp.h:
	Remove NR_VIRQS and NR_IPIS from FreeBSD headers.  NR_VIRQS
	is defined already for us in the xen interface files.
	NR_IPIS is only needed in one file per Xen platform and is
	easily inferred by the IPI vector table that is defined in
	those files.

sys/i386/xen/mp_machdep.c:
	Restructure to more closely match the HVM implementation by
	performing table driven IPI setup.