gma hsw: Enable Power Down Well for scaling on DDI A

The primary pipe can drive DDI A (eDP) without the Power Down
Well (PDW). The scalers are inside the PDW, though. To enable
scaling for DDI A, ensure the PDW is active.

When switching between scaled / unscaled modes, we'll have to
reconfigure the whole pipe.

Change-Id: I46318bb74d00a584d268a9d76787f8b26249264d
Signed-off-by: Nico Huber <nico.h@gmx.de>
Reviewed-on: https://review.coreboot.org/26663
Reviewed-by: Arthur Heymans <arthur@aheymans.xyz>
diff --git a/common/hw-gfx-gma-config.ads.template b/common/hw-gfx-gma-config.ads.template
index 1a4d124..46e2782 100644
--- a/common/hw-gfx-gma-config.ads.template
+++ b/common/hw-gfx-gma-config.ads.template
@@ -1,5 +1,5 @@
 --
--- Copyright (C) 2015-2017 secunet Security Networks AG
+-- Copyright (C) 2015-2018 secunet Security Networks AG
 --
 -- 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
@@ -47,6 +47,7 @@
                                                 (CPU in Haswell .. Broadwell);
    Pipe_Enabled_Workaround : constant Boolean := CPU = Broadwell;
    Has_EDP_Transcoder      : constant Boolean := CPU >= Haswell;
+   Use_PDW_For_EDP_Scaling : constant Boolean := CPU = Haswell;
    Has_Pipe_DDI_Func       : constant Boolean := CPU >= Haswell;
    Has_Trans_Clk_Sel       : constant Boolean := CPU >= Haswell;
    Has_Pipe_MSA_Misc       : constant Boolean := CPU >= Haswell;