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

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).]
Signed-off-by: Thomas Leonard <talex5@gmail.com>