media: rcar-vin: Refactor controls creation for video device

The controls for the video device are created in different code paths
depending on if the driver is using the media graph centric model (Gen3)
or the device centric model (Gen2 and earlier). This have lead to code
duplication that can be consolidated.

Signed-off-by: Niklas Söderlund <niklas.soderlund+renesas@ragnatech.se>
Reviewed-by: Jacopo Mondi <jacopo+renesas@jmondi.org>
Signed-off-by: Sakari Ailus <sakari.ailus@linux.intel.com>
Signed-off-by: Mauro Carvalho Chehab <mchehab+huawei@kernel.org>