[media] devicetree: bindings: Document Renesas R-Car JPEG Processing Unit

Add Renesas R-Car JPEG processing unit driver device tree bindings
documentation.

Signed-off-by: Mikhail Ulyanov <mikhail.ulyanov@cogentembedded.com>
Signed-off-by: Hans Verkuil <hans.verkuil@cisco.com>
Signed-off-by: Mauro Carvalho Chehab <mchehab@osg.samsung.com>