drm/vc4: hdmi: use drm_atomic_helper_connector_hdmi_hotplug()

drm/vc4: hdmi: use drm_atomic_helper_connector_hdmi_hotplug()

Use the helper function to update the connector's information. This
makes sure that HDMI-related events are handled in a generic way.
Currently it is limited to the HDMI state reporting to the sound system.

Acked-by: Maxime Ripard <mripard@kernel.org>
Tested-by: Dave Stevenson <dave.stevenson@raspberrypi.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20241224-drm-bridge-hdmi-connector-v10-10-dc89577cd438@linaro.org
Signed-off-by: Dmitry Baryshkov <dmitry.baryshkov@linaro.org>