Merge pull request #1 from jtdaugherty/minios-arm-port

Minios arm port
Added arch_endian.h for ARM
Disable memory test

Everything seems to be working now and the output clutters up the
console logs.
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.
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.
Merge pull request #2 from talex5/minios-arm-port

Fixes and updates for Mini-OS/arm32
Call exit_thread automatically when a thread returns

Also, tidied up thread switching with ldm/stm and made it pass the
thread's user data argument through to the thread.
Fixed HYPERVISOR_shutdown

Don't know what "low_shutdown" was supposed to do, but it doesn't exist.