agp/intel: Fix cache control for Sandybridge

Sandybridge GTT has new cache control bits in PTE, which controls
graphics page cache in LLC or LLC/MLC, so we need to extend the mask
function to respect the new bits.

And set cache control to always LLC only by default on Gen6.

Signed-off-by: Zhenyu Wang <zhenyuw@linux.intel.com>
Cc: stable@kernel.org
Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk>
diff --git a/drivers/gpu/drm/i915/i915_gem.c b/drivers/gpu/drm/i915/i915_gem.c
index 748c263..16fca1d 100644
--- a/drivers/gpu/drm/i915/i915_gem.c
+++ b/drivers/gpu/drm/i915/i915_gem.c
@@ -34,6 +34,7 @@
 #include <linux/slab.h>
 #include <linux/swap.h>
 #include <linux/pci.h>
+#include <linux/intel-gtt.h>
 
 static uint32_t i915_gem_get_gtt_alignment(struct drm_gem_object *obj);
 static int i915_gem_object_flush_gpu_write_domain(struct drm_gem_object *obj);