drm/virtio: move virtqueue_notify into virtio_gpu_queue_ctrl_sgs

It becomes clear that virtio_gpu_queue_fenced_ctrl_buffer should be
responsible for setting up sgs and virtio_gpu_queue_ctrl_sgs should
be responsible for queuing sgs.

Signed-off-by: Chia-I Wu <olvaffe@gmail.com>
Link: http://patchwork.freedesktop.org/patch/msgid/20200205181955.202485-11-olvaffe@gmail.com


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