Update qemu command line options for arm64
Update qemu command line options for arm64

- also allow arch context to be set to aarch64 or arm64

Change-Id: I8c3149a429ca3955f8e879cfe1919681337d2696

Linaro/lava-server,Linaro/lava-server,Linaro/lava-server,Linaro/lava-server