[media] cec: add MEDIA_CEC_RC config option

Add an explicit config option to select whether the CEC remote control
messages are to be passed on to the RC subsystem or not.

Signed-off-by: Hans Verkuil <hans.verkuil@cisco.com>
Signed-off-by: Mauro Carvalho Chehab <mchehab@s-opensource.com>