[media] rcar-vin: move media bus information to struct rvin_graph_entity

The primary reason for this change is to prepare for Gen3 support where
there will be more then one possible video source. Each source will have
its own media bus format and code, so it needs to be moved from the per
device structure to a structure used to represent an individual
connection to a video source.

Signed-off-by: Niklas Söderlund <niklas.soderlund+renesas@ragnatech.se>
Signed-off-by: Hans Verkuil <hans.verkuil@cisco.com>
Signed-off-by: Mauro Carvalho Chehab <mchehab@s-opensource.com>