drm/i915: remove duplicate definition of for_each_power_domain

drm/i915: remove duplicate definition of for_each_power_domain

commit 5181ad30832c7d8381234bfb08563b3b6185d371
Author: Borun Fu <borun.fu@intel.com>
Date:   Sat Jul 12 10:02:27 2014 +0530

    drm/i915: Power gating display wells during i915_pm_suspend

moved for_each_power_domain from intel_display.c to i915_drv.h but we
still have the definition around in intel_display.c, due to a merge
conflict resolution gone wrong in

commit 3f7e892c36767b4c9c1cc3c41c70e179416bbb78
Merge: 34747cdb1aab 60721400b7ad
Author: Daniel Vetter <daniel.vetter@ffwll.ch>
Date:   Tue Jul 29 20:49:36 2014 +0200

    Merge remote-tracking branch 'airlied/drm-next' into drm-intel-next

Just remove the extra definition left behind.

Reviewed-by: Daniel Vetter <daniel.vetter@ffwll.ch>
Signed-off-by: Jani Nikula <jani.nikula@intel.com>
Link: http://patchwork.freedesktop.org/patch/msgid/1448383645-7615-1-git-send-email-jani.nikula@intel.com