drm/i915: Drop WaDisablePSDDualDispatchEnable:ivb for IVB GT2

Both Bspec and the W/A database state that WaDisablePSDDualDispatchEnable
is only needed for IVB GT1.

The only real confusion here is that the the W/A database also says to
write to the GT2 only register as well, which is strange if the W/A is
only for GT1.

Signed-off-by: Ville Syrjälä <ville.syrjala@linux.intel.com>
Reviewed-by: Rodrigo Vivi <rodrigo.vivi@gmail.com>
Signed-off-by: Daniel Vetter <daniel.vetter@ffwll.ch>

drivers/gpu/drm/i915/intel_pm.c

@@ -4825,13 +4825,6 @@ static void ivybridge_init_clock_gating(struct drm_device *dev)
 	if (IS_IVB_GT1(dev))
 		I915_WRITE(GEN7_HALF_SLICE_CHICKEN1,
 			   _MASKED_BIT_ENABLE(GEN7_PSD_SINGLE_PORT_DISPATCH_ENABLE));
-	else {
-		/* must write both registers */
-		I915_WRITE(GEN7_HALF_SLICE_CHICKEN1,
-			   _MASKED_BIT_ENABLE(GEN7_PSD_SINGLE_PORT_DISPATCH_ENABLE));
-		I915_WRITE(GEN7_HALF_SLICE_CHICKEN1_GT2,
-			   _MASKED_BIT_ENABLE(GEN7_PSD_SINGLE_PORT_DISPATCH_ENABLE));
-	}
 
 	/* Apply the WaDisableRHWOOptimizationForRenderHang:ivb workaround. */
 	I915_WRITE(GEN7_COMMON_SLICE_CHICKEN1,