drm/i915: Include TLB miss latency in g4x watermark computations

Reports of FIFO underruns are still persisting on gm45.

References: https://bugs.freedesktop.org/show_bug.cgi?id=27589
Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk>
diff --git a/drivers/gpu/drm/i915/intel_drv.h b/drivers/gpu/drm/i915/intel_drv.h
index 74db255..5ce4a5f 100644
--- a/drivers/gpu/drm/i915/intel_drv.h
+++ b/drivers/gpu/drm/i915/intel_drv.h
@@ -217,6 +217,13 @@
 	return dev_priv->pipe_to_crtc_mapping[pipe];
 }
 
+static inline struct drm_crtc *
+intel_get_crtc_for_plane(struct drm_device *dev, int plane)
+{
+	struct drm_i915_private *dev_priv = dev->dev_private;
+	return dev_priv->plane_to_crtc_mapping[plane];
+}
+
 struct intel_unpin_work {
 	struct work_struct work;
 	struct drm_device *dev;