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 8192M -nographic

Change-Id: Id7c0831b1ecf08785b4ec8139d809bad9b3e1eec
Signed-off-by: Asami Doi <d0iasm.pub@gmail.com>
Reviewed-on: https://review.coreboot.org/c/coreboot/+/33387
Tested-by: build bot (Jenkins) <no-reply@coreboot.org>
Reviewed-by: Raul Rangel <rrangel@chromium.org>
Reviewed-by: Julius Werner <jwerner@chromium.org>
diff --git a/src/mainboard/emulation/qemu-aarch64/mainboard.c b/src/mainboard/emulation/qemu-aarch64/mainboard.c
new file mode 100644
index 0000000..5735455
--- /dev/null
+++ b/src/mainboard/emulation/qemu-aarch64/mainboard.c
@@ -0,0 +1,23 @@
+/*
+ * This file is part of the coreboot project.
+ *
+ * Copyright (C) 2019 Asami Doi <d0iasm.pub@gmail.com>
+ *
+ * SPDX-License-Identifier: GPL-2.0-or-later
+ */
+
+#include <cbmem.h>
+#include <ramdetect.h>
+#include <symbols.h>
+#include <device/device.h>
+
+static void mainboard_enable(struct device *dev)
+{
+	int ram_size_mb = probe_ramsize((uintptr_t)_dram, CONFIG_DRAM_SIZE_MB);
+	ram_resource(dev, 0, (uintptr_t)_dram / KiB, ram_size_mb * KiB);
+}
+
+struct chip_operations mainboard_ops = {
+	.name = "qemu_aarch64",
+	.enable_dev = mainboard_enable,
+};