media: rcar-vin: Only expose VIN controls

Before moving Gen2 to media controller simplify the creation of controls
by not exposing the sub-device controls on the video device. This could
be done while enabling media controller but doing it separately reduces
the changes needed to do so.

The rework also allows the cleanup and remove paths to be simplified by
folding all special cases into the only remaining call site.

Signed-off-by: Niklas Söderlund <niklas.soderlund+renesas@ragnatech.se>
Reviewed-by: Laurent Pinchart <laurent.pinchart+renesas@ideasonboard.com>
Link: https://lore.kernel.org/r/20250613153434.2001800-12-niklas.soderlund+renesas@ragnatech.se


Signed-off-by: Laurent Pinchart <laurent.pinchart@ideasonboard.com>
Signed-off-by: Hans Verkuil <hverkuil@xs4all.nl>