[media] media: i2c: adv7604: Use v4l2-dv-timings helpers

Use the helper to enumerate and set DV timings instead of a custom code.
This will ease debugging too, as it is consistent with other drivers.

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>