[media] stih-cec: add CEC notifier support

By using the CEC notifier framework there is no longer any reason
to manually set the physical address. This was the one blocking
issue that prevented this driver from going out of staging, so do
this move as well.

Signed-off-by: Benjamin Gaignard <benjamin.gaignard@linaro.org>
Signed-off-by: Hans Verkuil <hans.verkuil@cisco.com>
Signed-off-by: Mauro Carvalho Chehab <mchehab@s-opensource.com>