[media] media/uapi/v4l: clarify cropcap/crop/selection behavior

Unfortunately the use of 'type' was inconsistent for multiplanar
buffer types. Starting with 4.13 both the normal and _MPLANE variants
are allowed, thus making it possible to write sensible code.

Yes, we messed up :-(

Signed-off-by: Hans Verkuil <hans.verkuil@cisco.com>
Reviewed-by: Sylwester Nawrocki <s.nawrocki@samsung.com>
Acked-by: Sakari Ailus <sakari.ailus@linux.intel.com>
[hans.verkuil@cisco.com: 4.14 -> 4.13 since this would go in for 4.13 after all]

Signed-off-by: Mauro Carvalho Chehab <mchehab@s-opensource.com>