drm/tegra: Use cec_notifier_conn_(un)register()

Use the new cec_notifier_conn_(un)register() functions to
(un)register the notifier for the HDMI connector, and fill in
the cec_connector_info.

Signed-off-by: Dariusz Marcinkiewicz <darekm@google.com>
Tested-by: Hans Verkuil <hverkuil-cisco@xs4all.nl>
Acked-by: Hans Verkuil <hverkuil-cisco@xs4all.nl>
Signed-off-by: Thierry Reding <treding@nvidia.com>