Revert "drm/i915: Enable RC6 on Ironlake."

This reverts commit ce171780.

This commit has been independently bisected a few times as being the cause
of a s2ram failure.
Reported-and-tested-by: Kyle McMartin <kyle@mcmartin.ca>
Reported-and-tested-by: Andy Isaacson <adi@hexapodia.org>
Cc: Zou Nan hai <nanhai.zou@intel.com>
Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk>

drivers/gpu/drm/i915/intel_display.c

@@ -5696,7 +5696,6 @@ void intel_init_clock_gating(struct drm_device *dev)
 				   ILK_DPFC_DIS2 |
 				   ILK_CLK_FBC);
 		}
-		if (IS_GEN6(dev))
 		return;
 	} else if (IS_G4X(dev)) {
 		uint32_t dspclk_gate;
@@ -5758,11 +5757,9 @@ void intel_init_clock_gating(struct drm_device *dev)
 				OUT_RING(MI_FLUSH);
 				ADVANCE_LP_RING();
 			}
-		} else {
+		} else
 			DRM_DEBUG_KMS("Failed to allocate render context."
 				       "Disable RC6\n");
-			return;
-		}
 	}
 
 	if (I915_HAS_RC6(dev) && drm_core_check_feature(dev, DRIVER_MODESET)) {