Following the support for fences on the virtio driver add support
for native fence on virgl. This was somewhat based on the freedeno one.

Signed-off-by: Gustavo Padovan <gustavo.padovan@collabora.com>
Signed-off-by: Robert Foss <robert.foss@collabora.com>
Reviewed-by: Emil Velikov <emil.velikov@collabora.com>