[media] V4L: ov2640: support the new mbus-config subdev ops

Extend the driver to also support [gs]_mbus_config() subdevice video
operations.

Signed-off-by: Guennadi Liakhovetski <g.liakhovetski@gmx.de>
Signed-off-by: Mauro Carvalho Chehab <mchehab@redhat.com>