drm/virtio: Add the fence in resource_flush if present

If the framebuffer associated with the plane contains a fence, then
it is added to resource_flush and will be waited upon for a max of
50 msecs or until it is signalled by the Host.

Cc: Gerd Hoffmann <kraxel@redhat.com>
Signed-off-by: Vivek Kasireddy <vivek.kasireddy@intel.com>
Link: http://patchwork.freedesktop.org/patch/msgid/20210610232456.671905-4-vivek.kasireddy@intel.com


Signed-off-by: Gerd Hoffmann <kraxel@redhat.com>