Check if virtio-gpu provides virgl option, and add qemu command line
formatter.

It is enabled with the existing accel3d attribute:
<model type='virtio' heads='1'>
 <acceleration accel3d='yes'/>
</model>
Signed-off-by: NMarc-André Lureau <marcandre.lureau@gmail.com>
Signed-off-by: NMichal Privoznik <mprivozn@redhat.com>

qemu 2.5 provides virtio video device.  It can be used with -device
virtio-vga for primary devices, or -device virtio-gpu for non-vga
devices. However, only the primary device (VGA) is supported with this
patch.

Reference:
https://bugzilla.redhat.com/show_bug.cgi?id=1195176Signed-off-by: NMarc-André Lureau <marcandre.lureau@gmail.com>
Signed-off-by: NMichal Privoznik <mprivozn@redhat.com>

Signed-off-by: NJiri Denemark <jdenemar@redhat.com>

Allow setting vgamem size for video devices.

Resolves: https://bugzilla.redhat.com/show_bug.cgi?id=1076098Signed-off-by: NPavel Hrdina <phrdina@redhat.com>