drm/i915: don't save/restore CACHE_MODE_0 on gen7+

On gen7+, CACHE_MODE_0 moved, so we're clobbering some other reg rather
than restoring CACHE_MODE_0.  Don't do that.
Signed-off-by: Jesse Barnes <jbarnes@virtuousgeek.org>
Reviewed-by: Paulo Zanoni <paulo.r.zanoni@intel.com>
Signed-off-by: Daniel Vetter <daniel.vetter@ffwll.ch>

drivers/gpu/drm/i915/i915_suspend.c

@@ -369,6 +369,7 @@ int i915_save_state(struct drm_device *dev)
 	intel_disable_gt_powersave(dev);
 
 	/* Cache mode state */
+	if (INTEL_INFO(dev)->gen < 7)
 		dev_priv->regfile.saveCACHE_MODE_0 = I915_READ(CACHE_MODE_0);
 
 	/* Memory Arbitration state */
@@ -418,7 +419,9 @@ int i915_restore_state(struct drm_device *dev)
 	}
 
 	/* Cache mode state */
-	I915_WRITE(CACHE_MODE_0, dev_priv->regfile.saveCACHE_MODE_0 | 0xffff0000);
+	if (INTEL_INFO(dev)->gen < 7)
+		I915_WRITE(CACHE_MODE_0, dev_priv->regfile.saveCACHE_MODE_0 |
+			   0xffff0000);
 
 	/* Memory arbitration state */
 	I915_WRITE(MI_ARB_STATE, dev_priv->regfile.saveMI_ARB_STATE | 0xffff0000);