dp_info: read eDP 1.4+ DPCD link rates

This is required for google/eve (Pixelbook), where only this new
method of reporting the link rate is supported, and the
Max_Link_Rate in the regular DPCD struct is 0x00.

Change-Id: I52b4d8ad94564904854b502f300b812c41a9751a
Signed-off-by: Greg V <greg@unrelenting.technology>
Reviewed-on: https://review.coreboot.org/c/libgfxinit/+/35869
Tested-by: Nico Huber <nico.h@gmx.de>
Reviewed-by: Nico Huber <nico.h@gmx.de>
diff --git a/common/hw-gfx-dp_info.ads b/common/hw-gfx-dp_info.ads
index aa10c4c..6d22bcc 100644
--- a/common/hw-gfx-dp_info.ads
+++ b/common/hw-gfx-dp_info.ads
@@ -81,6 +81,10 @@
       Port     : in     T;
       Success  :    out Boolean);
 
+   procedure Read_eDP_Rates
+     (Link     : in out DP_Link;
+      Port     : in     T);
+
    procedure Preferred_Link_Setting
      (Link        : in out DP_Link;
       Mode        : in     Mode_Type;