media: rcar-vin: move media bus configuration to struct rvin_dev

Bus configuration will once the driver is extended to support Gen3
contain information not specific to only the directly connected parallel
subdevice. Move it to struct rvin_dev to show it's not always coupled
to the parallel subdevice.

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