drm/i915: use gen6 stolen check on VLV

It uses the same bit definitions.

Signed-off-by: Jesse Barnes <jbarnes@virtuousgeek.org>
Reviewed-by: Ville Syrjälä <ville.syrjala@linux.intel.com>
Signed-off-by: Daniel Vetter <daniel.vetter@ffwll.ch>

drivers/gpu/drm/i915/i915_gem_gtt.c

@@ -752,7 +752,7 @@ static int gen6_gmch_probe(struct drm_device *dev,
 	pci_read_config_word(dev->pdev, SNB_GMCH_CTRL, &snb_gmch_ctl);
 	gtt_size = gen6_get_total_gtt_size(snb_gmch_ctl);
 
-	if (IS_GEN7(dev))
+	if (IS_GEN7(dev) && !IS_VALLEYVIEW(dev))
 		*stolen = gen7_get_stolen_size(snb_gmch_ctl);
 	else
 		*stolen = gen6_get_stolen_size(snb_gmch_ctl);