[media] s5p-tv: mixer: Switch to pad-level DV operations

The video-level enum_dv_timings and dv_timings_cap operations are
deprecated in favor of the pad-level versions. All subdev drivers
implement the pad-level versions, switch to them.

Signed-off-by: Laurent Pinchart <laurent.pinchart@ideasonboard.com>
Reviewed-by: Hans Verkuil <hans.verkuil@cisco.com>
Signed-off-by: Mauro Carvalho Chehab <m.chehab@samsung.com>