drm/i915/hdmi: Nuke hdmi->ddc_bus

Remove the mostly redundant hdmi->ddc_bus. The only thing that needs
it anymore is get_encoder_by_ddc_bus(), but that can be replaced with
a slight detour through attached_connector+intel_gmbus_get_adapter().

Signed-off-by: Ville Syrjälä <ville.syrjala@linux.intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20230829113920.13713-11-ville.syrjala@linux.intel.com


Reviewed-by: Jani Nikula <jani.nikula@intel.com>