drm/i915: set the right gen3 flip_done mode also at resume

Currently we've only frobbed this bit at irq_init time, but did
not restore it at resume time. Move it to the gen3 clock gating
function to fix this.

Notice while reading through code.

Cc: stable@vger.kernel.org (for 3.5 only)
Reviewed-by: Chris Wilson <chris@chris-wilson.co.uk>
Signed-off-by: Daniel Vetter <daniel.vetter@ffwll.ch>
diff --git a/drivers/gpu/drm/i915/intel_pm.c b/drivers/gpu/drm/i915/intel_pm.c
index 1881c8c..ba8a27b 100644
--- a/drivers/gpu/drm/i915/intel_pm.c
+++ b/drivers/gpu/drm/i915/intel_pm.c
@@ -3672,6 +3672,9 @@
 
 	if (IS_PINEVIEW(dev))
 		I915_WRITE(ECOSKPD, _MASKED_BIT_ENABLE(ECO_GATING_CX_ONLY));
+
+	/* IIR "flip pending" means done if this bit is set */
+	I915_WRITE(ECOSKPD, _MASKED_BIT_DISABLE(ECO_FLIP_DONE));
 }
 
 static void i85x_init_clock_gating(struct drm_device *dev)