drm/i915: Set the required VFMUNIT clock gating disable on Ironlake.

It's required by the specs, but we don't know why.  Let's not find out
why.

Signed-off-by: Eric Anholt <eric@anholt.net>
Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk>
diff --git a/drivers/gpu/drm/i915/intel_display.c b/drivers/gpu/drm/i915/intel_display.c
index d9b7092..97e374e 100644
--- a/drivers/gpu/drm/i915/intel_display.c
+++ b/drivers/gpu/drm/i915/intel_display.c
@@ -5825,6 +5825,8 @@
 			I915_WRITE(PCH_3DCGDIS0,
 				   MARIUNIT_CLOCK_GATE_DISABLE |
 				   SVSMUNIT_CLOCK_GATE_DISABLE);
+			I915_WRITE(PCH_3DCGDIS1,
+				   VFMUNIT_CLOCK_GATE_DISABLE);
 		}
 
 		I915_WRITE(PCH_DSPCLK_GATE_D, dspclk_gate);