DNU: defconfig: arm64/x86_64: Enable virtio-msg and qemu/xen options

Turn on the virtio-msg transport pieces plus the qemu/xen config knobs
needed for the current development setup so both arm64 and x86_64
defconfigs can boot the virtio-msg test environment.

Signed-off-by: Viresh Kumar <viresh.kumar@linaro.org>