nb/intel/gm45: Set display backlight according to EDID string

Add some known good values for some thinkpads displays.

Known good means that at this pwm frequency the display is evenly lit
on all duty cycles, the display makes minimal to no noise at lower
duty cycles and the display does not flicker. This values differs from
vendor (which uses an obviously wrong display clock  (190MHz instead
of 320MHz) resulting in frequency more than 60% off the intended
value.

TESTED on Thinkpad X200 with edid ascii string in list and removed
from list to see if notice message is shown.

Change-Id: Id7bc0d453fac31e806852206ba2c895720b2c843
Signed-off-by: Arthur Heymans <arthur@aheymans.xyz>
Reviewed-on: https://review.coreboot.org/19500
Tested-by: build bot (Jenkins) <no-reply@coreboot.org>
Reviewed-by: Nico Huber <nico.h@gmx.de>

src/mainboard/roda/rk9/Makefile.inc

@@ -15,3 +15,4 @@
 
 ramstage-$(CONFIG_CARDBUS_PLUGIN_SUPPORT) += ti_pci7xx1.c
 ramstage-y += cstates.c
+ramstage-y += blc.c

src/mainboard/roda/rk9/blc.c

@@ -0,0 +1,22 @@
+/*
+ * This file is part of the coreboot project.
+ *
+ * Copyright (C) 2017 arthur@aheymans.xyz
+ *
+ * This program is free software; you can redistribute it and/or modify
+ * it under the terms of the GNU General Public License as published by
+ * the Free Software Foundation; version 2 of the License.
+ *
+ * This program is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ * GNU General Public License for more details.
+ */
+
+#include <stdint.h>
+#include <northbridge/intel/gm45/gm45.h>
+
+int get_blc_values(const struct blc_pwm_t **entries)
+{
+	return 0;
+}