drm/i915: Implement audio fastset

There's no real reason why we'd need a full modeset for audio
changes. So let's allow audio to be toggled during fastset.
In case the ELD changes while has_audio isn't changing state
we force both audio disable and enable so the new ELD gets
propagated to the audio driver.

Reviewed-by: Jani Nikula <jani.nikula@intel.com>
Signed-off-by: Ville Syrjälä <ville.syrjala@linux.intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20231121054324.9988-12-ville.syrjala@linux.intel.com