Merge tag 'drm-intel-fixes-2015-03-05' of git://anongit.freedesktop.org/drm-intel into drm-fixes

two fixes, both cc'd stable.

* tag 'drm-intel-fixes-2015-03-05' of git://anongit.freedesktop.org/drm-intel:
  drm/i915: gen4: work around hang during hibernation
  drm/i915: Check for driver readyness before handling an underrun interrupt