drm/vc4: hdmi: switch to generic CEC helpers

drm/vc4: hdmi: switch to generic CEC helpers

Switch VC4 driver to using CEC helpers code, simplifying hotplug and
registration / cleanup. The existing vc4_hdmi_cec_release() is kept for
now.

Signed-off-by: Dmitry Baryshkov <dmitry.baryshkov@linaro.org>
Reviewed-by: Maxime Ripard <mripard@kernel.org>
Tested-by: Dave Stevenson <dave.stevenson@raspberrypi.com>
Link: https://lore.kernel.org/r/20250705-drm-hdmi-connector-cec-v7-1-d14fa0c31b74@oss.qualcomm.com
Signed-off-by: Dmitry Baryshkov <dmitry.baryshkov@oss.qualcomm.com>