drm/bridge: lontium-lt9611uxc: switch to HDMI audio helpers

drm/bridge: lontium-lt9611uxc: switch to HDMI audio helpers

While LT9611UXC is a DSI-to-HDMI bridge, it implements all HDMI-related
functions internally, in the firmware, thus it doesn't make sense to
implement DRM_BRIDGE_OP_HDMI. However it is possible to implement
DRM_BRIDGE_OP_HDMI_AUDIO, streamlining HDMI audio plumbing (which
includes plugged notifications and ELD handling).

Implement corresponding callbacks and trigger EDID read /
drm_connector_hdmi_audio_plugged_notify() from the hpd_notify callback.

Reviewed-by: Neil Armstrong <neil.armstrong@linaro.org>
Link: https://patch.msgid.link/20250803-lt9611uxc-hdmi-v1-2-cb9ce1793acf@oss.qualcomm.com
Signed-off-by: Dmitry Baryshkov <dmitry.baryshkov@oss.qualcomm.com>