drm: Introduce a crtc_clock for struct drm_display_mode

Just like the various timings, make it possible to have a clock field
what we can tweak before giving it to hardware.

Reviewed-by: Ville Syrjälä <ville.syrjala@linux.intel.com>
Signed-off-by: Damien Lespiau <damien.lespiau@intel.com>
Acked-by: Dave Airlie <airlied@gmail.com>
Signed-off-by: Daniel Vetter <daniel.vetter@ffwll.ch>
diff --git a/include/drm/drm_crtc.h b/include/drm/drm_crtc.h
index 8e9716e..73478bc 100644
--- a/include/drm/drm_crtc.h
+++ b/include/drm/drm_crtc.h
@@ -156,6 +156,7 @@
 	int height_mm;
 
 	/* Actual mode we give to hw */
+	int crtc_clock;		/* in KHz */
 	int crtc_hdisplay;
 	int crtc_hblank_start;
 	int crtc_hblank_end;