drm/i915: Push audio_{enable,disable}() to the pre/post pane update stage

Relocate the audio enable/disable from the full modeset hooks into
the common pre/post plane update stage of the commit. Audio fastset
is within easy reach now.

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/20231121054324.9988-11-ville.syrjala@linux.intel.com