drm/virtio: virtio_{blah} --> virtio_gpu_{blah}

virtio_gpu typically uses the prefix virtio_gpu, but there are
a few places where the virtio prefix is used.  Modify this for
consistency.

v3: add r-b tags

Signed-off-by: Gurchetan Singh <gurchetansingh@chromium.org>
Reviewed-by: Anthoine Bourgeois <anthoine.bourgeois@gmail.com>
Link: http://patchwork.freedesktop.org/patch/msgid/20201201021623.619-1-gurchetansingh@chromium.org


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