drm/i915: Warn when cdclk for the platforms is not known

Print a warning if we fall through the .get_display_clock_speed() function
pointer setup. We end up assuming a 133MHz cdclk which should mean that
at least we avoid any 0 deivisions and whatnot. But this could at least
help remind people that they have to provide this function for new platforms.

v2: Rebased to the latest
v3: Rebased to the latest

Signed-off-by: Ville Syrjälä <ville.syrjala@linux.intel.com> (v1)
Signed-off-by: NMika Kahola <mika.kahola@intel.com>
Reviewed-by: NDamien Lespiau <damien.lespiau@intel.com>
Signed-off-by: NDaniel Vetter <daniel.vetter@ffwll.ch>

drivers/gpu/drm/i915/intel_display.c

@@ -14598,9 +14598,11 @@ static void intel_init_display(struct drm_device *dev)
 	else if (IS_I85X(dev))
 		dev_priv->display.get_display_clock_speed =
 			i85x_get_display_clock_speed;
-	else /* 830 */
+	else { /* 830 */
+		WARN(!IS_I830(dev), "Unknown platform. Assuming 133 MHz CDCLK\n");
 		dev_priv->display.get_display_clock_speed =
 			i830_get_display_clock_speed;
+	}
 
 	if (IS_GEN5(dev)) {
 		dev_priv->display.fdi_link_train = ironlake_fdi_link_train;