drm/i915: Add ECOBITS_SNB_BIT

GAC_ECO_BITS has a bit similar to GAM_ECOCHK's ECOCHK_SNB_BIT. Add
the define, and enable it on SNB.
Signed-off-by: Ville Syrjälä <ville.syrjala@linux.intel.com>
Reviewed-by: Imre Deak <imre.deak@intel.com>
Signed-off-by: Daniel Vetter <daniel.vetter@ffwll.ch>

drivers/gpu/drm/i915/i915_gem_gtt.c

@@ -106,7 +106,8 @@ static int gen6_ppgtt_enable(struct drm_device *dev)
 		uint32_t ecochk, gab_ctl, ecobits;
 
 		ecobits = I915_READ(GAC_ECO_BITS);
-		I915_WRITE(GAC_ECO_BITS, ecobits | ECOBITS_PPGTT_CACHE64B);
+		I915_WRITE(GAC_ECO_BITS, ecobits | ECOBITS_SNB_BIT |
+					 ECOBITS_PPGTT_CACHE64B);
 
 		gab_ctl = I915_READ(GAB_CTL);
 		I915_WRITE(GAB_CTL, gab_ctl | GAB_CTL_CONT_AFTER_PAGEFAULT);

drivers/gpu/drm/i915/i915_reg.h

@@ -127,6 +127,7 @@
 #define   ECOCHK_PPGTT_CACHE4B		(0x0<<3)
 
 #define GAC_ECO_BITS			0x14090
+#define   ECOBITS_SNB_BIT		(1<<13)
 #define   ECOBITS_PPGTT_CACHE64B	(3<<8)
 #define   ECOBITS_PPGTT_CACHE4B		(0<<8)