media: cec-notifier: add new notifier functions

In order to support multiple CEC devices for an HDMI connector,
and to support cec_connector_info, drivers should use either a
cec_notifier_conn_(un)register pair of functions (HDMI drivers)
or a cec_notifier_cec_adap_(un)register pair (CEC adapter drivers).

This replaces cec_notifier_get_conn/cec_notifier_put.

For CEC adapters it is also no longer needed to call cec_notifier_register,
cec_register_cec_notifier and cec_notifier_unregister. This is now
all handled internally by the new functions.

Signed-off-by: Hans Verkuil <hverkuil-cisco@xs4all.nl>
Signed-off-by: Mauro Carvalho Chehab <mchehab+samsung@kernel.org>