media: rcar-vin: add flag to switch to media controller mode

On Gen3 a media controller API needs to be used to allow userspace to
configure the subdevices in the pipeline instead of directly controlling
a single source subdevice, which is and will continue to be the mode of
operation on Gen2.

Prepare for these two modes of operation by adding a flag to struct
rvin_info which will control which mode to use.

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>