default-configs: Add config for aarch64-softmmu

Add a config for aarch64-softmmu; this enables building of this target.
The resulting executable doesn't know about any 64 bit CPUs, but all
the 32 bit CPUs and board models work.
Signed-off-by: NPeter Maydell <peter.maydell@linaro.org>
Message-id: 1385645602-18662-8-git-send-email-peter.maydell@linaro.org
Reviewed-by: NPeter Crosthwaite <peter.crosthwaite@xilinx.com>

default-configs/aarch64-softmmu.mak

+# Default configuration for aarch64-softmmu
+
+# We support all the 32 bit boards so need all their config
+include arm-softmmu.mak
+
+# Currently no 64-bit specific config requirements