drm/i915: hdmi: add CEC notifier to intel_hdmi

This patchs adds the cec_notifier feature to the intel_hdmi part
of the i915 DRM driver. It uses the HDMI DRM connector name to differentiate
between each HDMI ports.
The changes will allow the i915 HDMI code to notify EDID and HPD changes
to an eventual CEC adapter.

Signed-off-by: Neil Armstrong <narmstrong@baylibre.com>
Reviewed-by: Hans Verkuil <hans.verkuil@cisco.com>
Reviewed-by: Ville Syrjälä <ville.syrjala@linux.intel.com>
Acked-by: Rodrigo Vivi <rodrigo.vivi@intel.com>
Signed-off-by: Lee Jones <lee.jones@linaro.org>