[media] cec: adv7511: add cec support

Add CEC support to the adv7511 driver.

Signed-off-by: Hans Verkuil <hansverk@cisco.com>
[k.debski@samsung.com: Merged changes from CEC Updates commit by Hans Verkuil]
Signed-off-by: Kamil Debski <kamil@wypas.org>
Signed-off-by: Hans Verkuil <hans.verkuil@cisco.com>

Signed-off-by: Mauro Carvalho Chehab <mchehab@s-opensource.com>