[media] rc-cec: Add HDMI CEC keymap module

Add the keymap module for HDMI CEC remote control commands.

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>