[media] V4L2: Mark the DV Preset API as deprecated

The DV Preset API will be phased out in favor of the more flexible DV Timings
API. Mark the preset API accordingly in the header and documentation.

Signed-off-by: Hans Verkuil <hans.verkuil@cisco.com>
Signed-off-by: Mauro Carvalho Chehab <mchehab@redhat.com>