media: rcar-vin: Gen3 can not scale NV12

The VIN modules on Gen3 can not scale NV12, fail format validation if
the user tries. Currently no frames are produced if this is attempted.

Signed-off-by: Niklas Söderlund <niklas.soderlund+renesas@ragnatech.se>
Signed-off-by: Hans Verkuil <hverkuil-cisco@xs4all.nl>