[media] v4l2-subdev: add support for the new enum_frame_size 'which' field

Support the new 'which' field in the enum_frame_size ops. Most drivers do not
need to be changed since they always returns the same enumeration regardless
of the 'which' field.

Signed-off-by: Hans Verkuil <hans.verkuil@cisco.com>
Acked-by: Lad, Prabhakar <prabhakar.csengg@gmail.com>
Tested-by: Lad, Prabhakar <prabhakar.csengg@gmail.com>
Acked-by: Laurent Pinchart <laurent.pinchart@ideasonboard.com>
Acked-by: Sylwester Nawrocki <s.nawrocki@samsung.com>
Acked-by: Andrzej Hajda <a.hajda@samsung.com>
Signed-off-by: Mauro Carvalho Chehab <mchehab@osg.samsung.com>