drm/i915: don't always do full mode sets when infoframes are enabled

Partial revert of

commit 20664591
Author: Jesse Barnes <jbarnes@virtuousgeek.org>
Date:   Wed Nov 5 14:26:09 2014 -0800

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

References: https://bugs.freedesktop.org/show_bug.cgi?id=86683


Signed-off-by: Jesse Barnes <jbarnes@virtuousgeek.org>
Tested-by: Li Xu <li.l.xu@intel.com>
Signed-off-by: Jani Nikula <jani.nikula@intel.com>