[media] media: i2c: ADV7604: Migrate to regmap

This is a preliminary patch in order to add support for ALSA.
It replaces all current i2c access with regmap.

Signed-off-by: Pablo Anton <pablo.anton@veo-labs.com>
Signed-off-by: Jean-Michel Hautbois <jean-michel.hautbois@veo-labs.com>
Signed-off-by: Hans Verkuil <hans.verkuil@cisco.com>
Signed-off-by: Mauro Carvalho Chehab <mchehab@osg.samsung.com>