[media] v4l2-subdev: support new 'which' field in enum_mbus_code

Support the new 'which' field in the enum_mbus_code ops. Most drivers do not
need to be changed since they always return 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>
Acked-by: Laurent Pinchart <laurent.pinchart@ideasonboard.com>
Signed-off-by: Mauro Carvalho Chehab <mchehab@osg.samsung.com>