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

Minios arm port
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.