drm/connector: add CEC-related fields

As a preparation to adding HDMI CEC helper code, add CEC-related fields
to the struct drm_connector. The callbacks abstract CEC infrastructure
in order to support CEC adapters and CEC notifiers in a universal way.

CEC data is a void pointer as it allows us to make CEC data
helper-specific. For example, currently it will be either cec_notifier
or cec_adapter + drm_connector_hdmi_cec_funcs. Later cec-pin might store
platform callbacks here. DP CEC might need to store AUX pointer, etc.

Signed-off-by: Dmitry Baryshkov <dmitry.baryshkov@linaro.org>
Reviewed-by: Maxime Ripard <mripard@kernel.org>
Link: https://lore.kernel.org/r/20250517-drm-hdmi-connector-cec-v6-3-35651db6f19b@oss.qualcomm.com


Signed-off-by: Dmitry Baryshkov <dmitry.baryshkov@oss.qualcomm.com>