[ARM] Add Raspberry Pi (or BCM2835 SOC) support

This is initial board support for Raspberry Pi or BCM2835 SOC.

This patch enables us to boot vmm.bin on Raspberry Pi emulated by QEMU.

The source for QEMU with Raspberry Pi support resides in rpi branch of https://github.com/Torlus/qemu

In future, we will be able to boot a ARMv6 guest on Raspberry Pi (emulated by QEMU or real HW).

Signed-off-by: Anup Patel <anup@brainfault.org>