ARM: qemu-arm: Add support for AArch64

This adds support for '-machine virt' on AArch64. This is rather simple:
we just add TARGET_QEMU_ARM_xxBIT to select a few different Kconfig
symbols, provide the ARMv8 memory map from the board file and add a new
defconfig based on the 32-bit defconfig.

Signed-off-by: Tuomas Tynkkynen <tuomas.tynkkynen@iki.fi>
Reviewed-by: Tom Rini <trini@konsulko.com>
diff --git a/configs/qemu_arm_defconfig b/configs/qemu_arm_defconfig
index 3cd4d45..db61b12 100644
--- a/configs/qemu_arm_defconfig
+++ b/configs/qemu_arm_defconfig
@@ -1,6 +1,7 @@
 CONFIG_ARM=y
 CONFIG_ARM_SMCCC=y
 CONFIG_ARCH_QEMU=y
+CONFIG_TARGET_QEMU_ARM_32BIT=y
 CONFIG_AHCI=y
 CONFIG_DISTRO_DEFAULTS=y
 # CONFIG_DISPLAY_CPUINFO is not set