arm: implement query-gic-capabilities

arm: implement query-gic-capabilities

For emulated GIC capabilities, currently only gicv2 is supported. We
need to add gicv3 in when emulated gicv3 ready. For KVM accelerated ARM
VM, we detect the capability bits by creating a scratch VM.

Signed-off-by: Peter Xu <peterx@redhat.com>
Acked-by: Sergey Fedorov <serge.fdrv@gmail.com>
Message-id: 1458788142-17509-5-git-send-email-peterx@redhat.com
Reviewed-by: Peter Maydell <peter.maydell@linaro.org>
Signed-off-by: Peter Maydell <peter.maydell@linaro.org>