media: v4l: link dt-bindings and uapi

Since we expose the definition to the dt-bindings we need to keep those
definitions in sync. To address this the patch adds a simple cross
reference to the dt-bindings.

Signed-off-by: Marco Felsch <m.felsch@pengutronix.de>
Signed-off-by: Hans Verkuil <hverkuil-cisco@xs4all.nl>
Signed-off-by: Mauro Carvalho Chehab <mchehab+huawei@kernel.org>