[media] vpbe_display: drop g/s_register ioctls

These are no longer needed: register access to subdevices no longer needs
the bridge driver to forward them.

Signed-off-by: Hans Verkuil <hans.verkuil@cisco.com>
Acked-by: Lad, Prabhakar <prabhakar.csengg@gmail.com>
Signed-off-by: Mauro Carvalho Chehab <mchehab@redhat.com>