[media] cx231xx: add media controller support

Let's add media controller support for this driver and register it
for both V4L and DVB.

The media controller on this driver is not mandatory, as it can fully
work without it. So, if the media controller register fails, just print
an error message, but proceed with device registering.

Signed-off-by: Mauro Carvalho Chehab <mchehab@osg.samsung.com>