[media] v4l: Image processing control class

Add control class for image processing controls. The control class deals
with controls processing image, for example digital gain or noise filtering,
which can be present in any part of the pipeline.

Signed-off-by: Sakari Ailus <sakari.ailus@iki.fi>
Signed-off-by: Mauro Carvalho Chehab <mchehab@redhat.com>