mini-os: build fixes

Make .o rules depend on the includes. Before, only the final link step
depended on setting up the includes directory, making the build
unreliable.

Make symlinks using explicit make rules instead of using a phony target.
Avoids unnecessary rebuilds.
mini-os: fixed shutdown thread

Before, it read "" and started a shutdown immediately. Now, it waits for
a non-empty value and then actually shuts down.

Signed-off-by: Thomas Leonard <talex5@gmail.com>
Acked-by: Samuel Thibault <samuel.thibault@ens-lyon.org>
mini-os: tidied up code

Signed-off-by: Karim Allah Ahmed <karim.allah.ahmed@gmail.com>
[talex5@gmail.com: separated from big ARM commit]
Acked-by: Samuel Thibault <samuel.thibault@ens-lyon.org>
[talex5@gmail.com: use __func__ in DEBUG macro]
[talex5@gmail.com: drop text about "xm create"]
Signed-off-by: Thomas Leonard <talex5@gmail.com>
mini-os: moved events code under arch

This is all code motion, except that we now initialise
the ev_actions array before calling the arch-specific code
to make it more robust against future changes.

Signed-off-by: Karim Allah Ahmed <karim.allah.ahmed@gmail.com>
[talex5@gmail.com: separated from big ARM commit]
Signed-off-by: Thomas Leonard <talex5@gmail.com>
mini-os: switched initial C entry point to arch_init

arch_print_info (a debug print called during start up) was also removed.

Signed-off-by: Karim Allah Ahmed <karim.allah.ahmed@gmail.com>
[talex5@gmail.com: separated from big ARM commit]
[talex5@gmail.com: restored comment, moved prototypes to headers]
Signed-off-by: Thomas Leonard <talex5@gmail.com>
mini-os: initial ARM support

On ARM, Mini-OS will boot and display some output on the console.
Tested with:

make XEN_TARGET_ARCH=arm32 CROSS_COMPILE=arm-linux-gnueabihf- \
  CONFIG_TEST=n CONFIG_START_NETWORK=n CONFIG_BLKFRONT=n \
  CONFIG_NETFRONT=n CONFIG_FBFRONT=n CONFIG_KBDFRONT=n \
  CONFIG_CONSFRONT=n CONFIG_XC=n CONFIG_XENBUS=n

Signed-off-by: Karim Allah Ahmed <karim.allah.ahmed@gmail.com>
[talex5@gmail.com: made x86_64 support work again]
[talex5@gmail.com: split into multiple patches]
[talex5@gmail.com: re-enabled force_evtchn_callback]
[talex5@gmail.com: enable regular console]
[talex5@gmail.com: fixed initialisation code:
- Configure write-back caching in page table. This is needed for
  reliable hypercalls to Xen (thanks to Julien Grall).
- Use "client mode" for access control (domains are deprecated,
  according to ARM Cortex-A Series Programmer’s Guide version 4.0,
  section 9.6.4).
- Enable more SCTLR features (icache, branch prediction)]
[talex5@gmail.com: use Virtual Count register for monotonic time]
[talex5@gmail.com: fixed HYPERVISOR_shutdown]
[talex5@gmail.com: get xenstore details from hypervisor]
Signed-off-by: Thomas Leonard <talex5@gmail.com>