gma hsw+: Add default value for HDMI buffer levels

Add a configuration option to override the default HDMI translation.
It's not exported yet, as we've never seen a non-default value being
used. So this is just to have a common place for the defaults.

Also sets the recommended default value for Broxton as defined in the
PRM.

Change-Id: I59fae0fb4f444d9193a98b6a0edf337ecbba3b62
Signed-off-by: Nico Huber <nico.huber@secunet.com>
Reviewed-on: https://review.coreboot.org/20165
Tested-by: Nico Huber <nico.h@gmx.de>
Reviewed-by: Stefan Reinauer <stefan.reinauer@coreboot.org>
diff --git a/common/hw-gfx-gma-config.ads.template b/common/hw-gfx-gma-config.ads.template
index 2bb916a..7d6806a 100644
--- a/common/hw-gfx-gma-config.ads.template
+++ b/common/hw-gfx-gma-config.ads.template
@@ -27,6 +27,8 @@
 
    EDP_Low_Voltage_Swing : constant Boolean := False;
 
+   DDI_HDMI_Buffer_Translation : constant Integer := -1;
+
    Default_MMIO_Base : constant := <<DEFAULT_MMIO_BASE>>;
 
    LVDS_Dual_Threshold : constant := 95_000_000;
@@ -206,6 +208,13 @@
 
    ----------------------------------------------------------------------------
 
+   Default_DDI_HDMI_Buffer_Translation : constant DDI_HDMI_Buf_Trans_Range :=
+     (case CPU is
+         when Broxton   => 8,
+         when others    => 0);
+
+   ----------------------------------------------------------------------------
+
    Default_CDClk_Freq : constant Frequency_Type :=
      (case CPU is
          when Ironlake     |