media: rcar-vin: Update format alignment constraints

This change fixes two issues with the size constraints for buffers.

- There is no width alignment constraint for RGB formats. Prior to this
  change they were treated as YUV and as a result were more restricted
  than needed. Add a new check to differentiate between the two.

- The minimum width and height supported is 5x2, not 2x4, this is an
  artifact from the driver's soc-camera days. Fix this incorrect
  assumption.

Signed-off-by: Niklas Söderlund <niklas.soderlund+renesas@ragnatech.se>
Signed-off-by: Hans Verkuil <hverkuil-cisco@xs4all.nl>
Signed-off-by: Mauro Carvalho Chehab <mchehab+huawei@kernel.org>