drm: dw-hdmi: use cec_notifier_conn_(un)register

drm: dw-hdmi: 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.

Changes since v6:
        - move cec_notifier_conn_unregister to a bridge detach
	  function,
	- add a mutex protecting a CEC notifier.
Changes since v4:
	- typo fix
Changes since v2:
	- removed unnecessary NULL check before a call to
	cec_notifier_conn_unregister,
	- use cec_notifier_phys_addr_invalidate to invalidate physical
	address.
Changes since v1:
	Add memory barrier to make sure that the notifier
	becomes visible to the irq thread once it is fully
	constructed.

Signed-off-by: Dariusz Marcinkiewicz <darekm@google.com>
Acked-by: Hans Verkuil <hverkuil-cisco@xs4all.nl>
Tested-by: Hans Verkuil <hverkuil-cisco@xs4all.nl>
Reviewed-by: Neil Armstrong <narmstrong@baylibre.com>
Signed-off-by: Neil Armstrong <narmstrong@baylibre.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20190814104520.6001-9-darekm@google.com