[media] rcar-vin: add R-Car gen2 fallback compatibility string

Such fallback string is present in the 'soc_camera' version of the R-Car VIN
driver, so need  to add it here as well...

Signed-off-by: Sergei Shtylyov <sergei.shtylyov@cogentembedded.com>
Acked-by: Niklas Söderlund <niklas.soderlund+renesas@ragnatech.se>
Signed-off-by: Mauro Carvalho Chehab <mchehab@s-opensource.com>