gma: Use framebuffer size as pipe source size

Now that we are going to use scaling and have framebuffer sizes dif-
ferent from the display mode's resolution, it's crucial to put the
right size (i.e. the unscaled framebuffer size) into PIPESRC.

Change-Id: Ieb4b5c3960490e286d44c982c28f7ff729ecd84b
Signed-off-by: Nico Huber <nico.huber@secunet.com>
Reviewed-on: https://review.coreboot.org/17264
Tested-by: Nico Huber <nico.h@gmx.de>
Reviewed-by: Arthur Heymans <arthur@aheymans.xyz>

common/hw-gfx-gma-pipe_setup.adb

@@ -339,7 +339,10 @@ package body HW.GFX.GMA.Pipe_Setup is
    begin
       pragma Debug (Debug.Put_Line (GNAT.Source_Info.Enclosing_Entity));
 
-      Registers.Write (Controller.PIPESRC, Encode (Mode.V_Visible, Mode.H_Visible));
+      Registers.Write
+        (Register => Controller.PIPESRC,
+         Value    => Encode
+           (Pos16 (Framebuffer.Height), Pos16 (Framebuffer.Width)));
 
       if Config.Has_Plane_Control then
          Setup_Watermarks (Controller);