drm/i915: apply HWSTAM writes to Ivy Bridge as well

In an attempt to fix 38862 and 38863.
Signed-off-by: NJesse Barnes <jbarnes@virtuousgeek.org>
Tested-by: NKenneth Graunke <kenneth@whitecape.org>
Signed-off-by: NKeith Packard <keithp@keithp.com>

drivers/gpu/drm/i915/i915_irq.c

@@ -1740,7 +1740,7 @@ static void ironlake_irq_preinstall(struct drm_device *dev)
 		INIT_WORK(&dev_priv->rps_work, gen6_pm_rps_work);
 
 	I915_WRITE(HWSTAM, 0xeffe);
-	if (IS_GEN6(dev)) {
+	if (IS_GEN6(dev) || IS_GEN7(dev)) {
 		/* Workaround stalls observed on Sandy Bridge GPUs by
 		 * making the blitter command streamer generate a
 		 * write to the Hardware Status Page for