V4L/DVB: soc_camera_platform: Add necessary v4l2_subdev_video_ops method

These function are needed to use camera.
This patch was tested with sh_mobile_ceu_camera

Signed-off-by: Kuninori Morimoto <kuninori.morimoto.gx@renesas.com>
Signed-off-by: Guennadi Liakhovetski <g.liakhovetski@gmx.de>
Signed-off-by: Mauro Carvalho Chehab <mchehab@redhat.com>