gma: Add support for ULX variants

On Haswell and Broadwell, the ULX variants differ only in the available
CD clock frequencies and, on Haswell, the maximum DP link rate. On newer
generations (Skylake+), they differ only in output buffer tuning.

Also update the PCI IDs from Haswell to Skylake.

Still untested, which was the original reason to skip ULX.

Change-Id: I08e6689ff8c0f2d58b51363886d4cab956f44e03
Signed-off-by: Nico Huber <nico.h@gmx.de>
Reviewed-on: https://review.coreboot.org/c/libgfxinit/+/31452
Reviewed-by: Thomas Heijligen <src@posteo.de>
Reviewed-by: Angel Pons <th3fanbus@gmail.com>
diff --git a/common/haswell_shared/hw-gfx-gma-connectors-ddi.adb b/common/haswell_shared/hw-gfx-gma-connectors-ddi.adb
index 7f179ff..7efb93f 100644
--- a/common/haswell_shared/hw-gfx-gma-connectors-ddi.adb
+++ b/common/haswell_shared/hw-gfx-gma-connectors-ddi.adb
@@ -298,7 +298,7 @@
 
    procedure Initialize
    is
-      Iboost_Value : constant Word32 := 1;
+      Iboost_Value : constant Word32 := Word32 (Config.DDI_Buffer_Iboost);
    begin
       if Config.Has_DDI_Buffer_Trans then
          declare