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=y CONFIG_START_NETWORK=n CONFIG_BLKFRONT=n \
	CONFIG_NETFRONT=n CONFIG_FBFRONT=n CONFIG_KBDFRONT=n \
	CONFIG_CONSFRONT=n CONFIG_XC=n -j4

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]
[talex5@gmail.com: use GCC implementation of division]
[talex5@gmail.com: include hypervisor.h from os.h, as on x86]
[talex5@gmail.com: cleaned up interrupt handlers and threading]
[talex5@gmail.com: call exit_thread when a thread returns]
[talex5@gmail.com: implemented block_domain for ARM]
[talex5@gmail.com: fixed hang when enabling interrupts]
[talex5@gmail.com: added -march=armv7-a to flags]
[talex5@gmail.com: implemented asm bitops]
[talex5@gmail.com: CLREX after handling IRQs]
[talex5@gmail.com: unbind debug port at shutdown]
Signed-off-by: Thomas Leonard <talex5@gmail.com>
mini-os: arm: show registers, stack and exception vector on fault

Signed-off-by: Thomas Leonard <talex5@gmail.com>
mini-os: import libfdt

Signed-off-by: Karim Allah Ahmed <karim.allah.ahmed@gmail.com>
[talex5@gmail.com: split out FDT support into a separate patch]
[talex5@gmail.com: fixed "make clean" for FDT]
Signed-off-by: Thomas Leonard <talex5@gmail.com>
mini-os: get RAM base and size from the FDT
mini-os: preserve device tree when initialising MM

Move the device tree to a reserved area at the end of the RAM.
mini-os: get GIC addresses from FDT
mini-os: added arch_endian.h for ARM
mini-os: added ARM grant table initialisation

On x86, we get told which pages to use, but on ARM we get the base
address in the FDT and have to map each page.
mini-os: networking on ARM

Set MEM_ALIGNMENT=4 to request word-aligned memory access. However, this
does not cover all cases in lwIP, so also configure the CPU to allow
unaligned accesses.
mini-os: reorganised arch headers

Before, we had:

- include
- include/arm
- include/x86

Where either arm or x86 was added directly to the search path. So
<x86/arch_limits.h> was the same file as <arch_limits.h> on x86.

We now have:

- include
- arch/arm/include
- arch/x86/include

This means that only the second form is now legal. It also simplifies
installation of the headers, since we can now install everything in the
include directory without getting files for other archs.
mini-os: added make install target

This installs libminios.a, the linker script, the headers and a
pkg-config file to locate them.
mini-os: expose gnttab_table, NR_GRANT_FRAMES, etc

Needed by Mirage.
Hacks for Mirage