This patch adds a virtio-vga device.  It is simliar to virtio-gpu-pci,
but it also adds in vga compatibility, so guests without native
virtio-gpu support can drive the device in vga mode.  It is compatible
with stdvga.

Written by Dave Airlie and Gerd Hoffmann.
Signed-off-by: NDave Airlie <airlied@redhat.com>
Signed-off-by: NGerd Hoffmann <kraxel@redhat.com>