drm/i915: check for audio and infoframe changes across mode sets v2

If these change (e.g. after a modeset following a fastboot), we need to
do a full mode set.

v2:
  - put under pipe_config check so we don't deref a null state (Jesse)

Signed-off-by: Jesse Barnes <jbarnes@virtuousgeek.org>
Reviewed-by: Ander Conselvan de Oliveira <ander.conselvan.de.oliveira@intel.com>
Signed-off-by: Daniel Vetter <daniel.vetter@ffwll.ch>