V4L/DVB (12158): v4l: add cropping prototypes to struct v4l2_subdev_video_ops

Add g_crop, s_crop and cropcap methods to video v4l2-subdev operations.

Signed-off-by: Guennadi Liakhovetski <g.liakhovetski@gmx.de>
Reviewed-by: Hans Verkuil <hverkuil@xs4all.nl>
Signed-off-by: Mauro Carvalho Chehab <mchehab@redhat.com>