media: seco-cec: use cec_notifier_cec_adap_(un)register

Use cec_notifier_cec_adap_(un)register instead of
cec_notifier_get_conn, cec_notifier_put and cec_register_cec_notifier.

Also enable the CEC_CAP_CONNECTOR_INFO capability.

Signed-off-by: Hans Verkuil <hverkuil-cisco@xs4all.nl>
Cc: Ettore Chimenti <ek5.chimenti@gmail.com>
Signed-off-by: Mauro Carvalho Chehab <mchehab+samsung@kernel.org>