mainboard/emulation/qemu-aarch64: Add new board for ARMv8

This CL adds a new board, QEMU/AArch64, for ARMv8. The machine supported
is virt which is a QEMU 2.8 ARM virtual machine. The default CPU of
qemu-system-aarch64 is Cortex-a15, so you need to specify a 64-bit cpu
via a flag.

To execute:
$ qemu-system-aarch64 -M virt,secure=on,virtualization=on \
  -cpu cortex-a53 -bios build/coreboot.rom -m 2048M -nographic

Change-Id: Id7c0831b1ecf08785b4ec8139d809bad9b3e1eec
Signed-off-by: Asami Doi <d0iasm.pub@gmail.com>
---
A Documentation/mainboard/emulation/qemu-aarch64.md
M Documentation/mainboard/index.md
A src/mainboard/emulation/qemu-aarch64/Kconfig
A src/mainboard/emulation/qemu-aarch64/Kconfig.name
A src/mainboard/emulation/qemu-aarch64/Makefile.inc
A src/mainboard/emulation/qemu-aarch64/board_info.txt
A src/mainboard/emulation/qemu-aarch64/bootblock_custom.S
A src/mainboard/emulation/qemu-aarch64/cbmem.c
A src/mainboard/emulation/qemu-aarch64/devicetree.cb
A src/mainboard/emulation/qemu-aarch64/exception.c
A src/mainboard/emulation/qemu-aarch64/include/mainboard/addressmap.h
A src/mainboard/emulation/qemu-aarch64/include/mainboard/exception.h
A src/mainboard/emulation/qemu-aarch64/mainboard.c
A src/mainboard/emulation/qemu-aarch64/media.c
A src/mainboard/emulation/qemu-aarch64/memlayout.ld
A src/mainboard/emulation/qemu-aarch64/mmio.c
16 files changed, 373 insertions(+), 0 deletions(-)