media: rcar-vin: Add support for R-Car V4H

Add support for R-Car V4H. The V4H uses the ISP Channel Selector as its
only possible video input source. Even tho V4H is a Gen3 board the VIN
interface is very close to the one found on the V3U, for this reason
mark it as a Gen3 model internally.

Signed-off-by: Niklas Söderlund <niklas.soderlund+renesas@ragnatech.se>
Signed-off-by: Sakari Ailus <sakari.ailus@linux.intel.com>
Signed-off-by: Hans Verkuil <hverkuil-cisco@xs4all.nl>