drm/i915: compute the target_clock for edp directly

... instead of abusing mode->clock by storing it in there - we
shouldn't touch that one at all. This patch is the first prep step to
constify the mode argument of the intel_dp_mode_fixup function.

The next patch will stop us from modifying mode->clock.

Reviewed-by: Chris Wilson <chris@chris-wilson.co.uk>
Reviewed-by: Jesse Barnes <jbarnes@virtuousgeek.org>
Signed-Off-by: Daniel Vetter <daniel.vetter@ffwll.ch>
diff --git a/drivers/gpu/drm/i915/intel_drv.h b/drivers/gpu/drm/i915/intel_drv.h
index 39d7b07..6a2ae30 100644
--- a/drivers/gpu/drm/i915/intel_drv.h
+++ b/drivers/gpu/drm/i915/intel_drv.h
@@ -359,6 +359,8 @@
 		 struct drm_display_mode *adjusted_mode);
 extern bool intel_dpd_is_edp(struct drm_device *dev);
 extern void intel_edp_link_config(struct intel_encoder *, int *, int *);
+extern int intel_edp_target_clock(struct intel_encoder *,
+				  struct drm_display_mode *mode);
 extern bool intel_encoder_is_pch_edp(struct drm_encoder *encoder);
 extern int intel_plane_init(struct drm_device *dev, enum pipe pipe);
 extern void intel_flush_display_plane(struct drm_i915_private *dev_priv,