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.