drm/i915: Undo "Uncouple render/power ctx before suspending"

Manaul revert of 0cdab21f, just to
remove the call to disable the clock gatings and powerctx before
suspend.

Peter Clifton bisected a suspend failure on his gme45 and found this to
be the culprit. As this was intended to be a fix for a similar suspend
failure for Ironlake (it didn't work), undoing this patch should have no
other side-effects.
Reported-and-tested-by: Peter Clifton <pcjc2@cam.ac.uk>
Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk>

drivers/gpu/drm/i915/i915_suspend.c

@@ -822,7 +822,9 @@ int i915_save_state(struct drm_device *dev)
 	if (IS_GEN6(dev))
 		gen6_disable_rps(dev);
 
+	/* XXX disabling the clock gating breaks suspend on gm45
 	intel_disable_clock_gating(dev);
+	 */
 
 	/* Cache mode state */
 	dev_priv->saveCACHE_MODE_0 = I915_READ(CACHE_MODE_0);