drm/nouveau: add DisplayPort CEC-Tunneling-over-AUX support

Add DisplayPort CEC-Tunneling-over-AUX support to nouveau.

Signed-off-by: Hans Verkuil <hans.verkuil@cisco.com>
Reviewed-by: Lyude Paul <lyude@redhat.com>
Acked-by: Alex Deucher <alexander.deucher@amd.com>
Link: https://patchwork.freedesktop.org/patch/msgid/5c0b907d-0bf2-7b80-b4b6-cbde78b03f0d@xs4all.nl