[media] adv7842: adjust gain and offset for DVI-D signals

If the input signal is DVI-D and quantization range is RGB full range,
gain and offset must be adjusted to get the right range on the output.
Copied and adopted from adv7604.

Signed-off-by: Martin Bugge <marbugge@cisco.com>
Cc: Mats Randgaard <matrandg@cisco.com>
Signed-off-by: Hans Verkuil <hans.verkuil@cisco.com>
Signed-off-by: Mauro Carvalho Chehab <m.chehab@samsung.com>