drm/i915: create macros to handle masked bits

... and put them to so good use.

Note that there's functional change in vlv clock gating code, we now
no longer spuriously read back the current value of the bit. According
to Bspec the high bits should always read zero, so ORing this in
should have no effect.

Reviewed-by: Jesse Barnes <jbarnes@virtuousgeek.org>
Reviewed-by: Chris Wilson <chris@chris-wilson.co.uk>
Reviewed-by: Eugeni Dodonov <eugeni.dodonov@intel.com>
Signed-Off-by: Daniel Vetter <daniel.vetter@ffwll.ch>
diff --git a/drivers/gpu/drm/i915/i915_gem.c b/drivers/gpu/drm/i915/i915_gem.c
index 38490cd..cfbcf7e 100644
--- a/drivers/gpu/drm/i915/i915_gem.c
+++ b/drivers/gpu/drm/i915/i915_gem.c
@@ -3494,9 +3494,9 @@
 
 	I915_WRITE(TILECTL, I915_READ(TILECTL) | TILECTL_SWZCTL);
 	if (IS_GEN6(dev))
-		I915_WRITE(ARB_MODE, ARB_MODE_ENABLE(ARB_MODE_SWIZZLE_SNB));
+		I915_WRITE(ARB_MODE, _MASKED_BIT_ENABLE(ARB_MODE_SWIZZLE_SNB));
 	else
-		I915_WRITE(ARB_MODE, ARB_MODE_ENABLE(ARB_MODE_SWIZZLE_IVB));
+		I915_WRITE(ARB_MODE, _MASKED_BIT_ENABLE(ARB_MODE_SWIZZLE_IVB));
 }
 
 void i915_gem_init_ppgtt(struct drm_device *dev)
@@ -3545,7 +3545,7 @@
 		ecochk = I915_READ(GAM_ECOCHK);
 		I915_WRITE(GAM_ECOCHK, ecochk | ECOCHK_SNB_BIT |
 				       ECOCHK_PPGTT_CACHE64B);
-		I915_WRITE(GFX_MODE, GFX_MODE_ENABLE(GFX_PPGTT_ENABLE));
+		I915_WRITE(GFX_MODE, _MASKED_BIT_ENABLE(GFX_PPGTT_ENABLE));
 	} else if (INTEL_INFO(dev)->gen >= 7) {
 		I915_WRITE(GAM_ECOCHK, ECOCHK_PPGTT_CACHE64B);
 		/* GFX_MODE is per-ring on gen7+ */
@@ -3556,7 +3556,7 @@
 
 		if (INTEL_INFO(dev)->gen >= 7)
 			I915_WRITE(RING_MODE_GEN7(ring),
-				   GFX_MODE_ENABLE(GFX_PPGTT_ENABLE));
+				   _MASKED_BIT_ENABLE(GFX_PPGTT_ENABLE));
 
 		I915_WRITE(RING_PP_DIR_DCLV(ring), PP_DIR_DCLV_2G);
 		I915_WRITE(RING_PP_DIR_BASE(ring), pd_offset);