gma: Refactor Hotplug_Detect() interface and usage

Checking for hotplug events should be done before any other work to
reduce load and (spurious) debug output. Therefor, use the simpler
`Port_Type` in the interface of `Hotplug_Detect()` so we don't have to
fill the whole `Port_Cfg` before checking for events.

Also, now that it's possible, factor the disabling of a single output
out of `Update_Outputs()`.

Change-Id: I2a0ba5530c8d511fa95f9cac12297ad428a40d77
Signed-off-by: Nico Huber <nico.huber@secunet.com>
Reviewed-on: https://review.coreboot.org/18119
Tested-by: Nico Huber <nico.h@gmx.de>
Reviewed-by: Patrick Georgi <pgeorgi@google.com>
diff --git a/common/hw-gfx-gma-config_helpers.ads b/common/hw-gfx-gma-config_helpers.ads
index b56e1b1..1029177 100644
--- a/common/hw-gfx-gma-config_helpers.ads
+++ b/common/hw-gfx-gma-config_helpers.ads
@@ -1,5 +1,5 @@
 --
--- Copyright (C) 2015-2016 secunet Security Networks AG
+-- Copyright (C) 2015-2017 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
@@ -17,6 +17,11 @@
 private package HW.GFX.GMA.Config_Helpers
 is
 
+   function To_GPU_Port
+     (Pipe  : Pipe_Index;
+      Port  : Active_Port_Type)
+      return GPU_Port;
+
    function To_PCH_Port (Port : Active_Port_Type) return PCH_Port;
 
    function To_Display_Type (Port : Active_Port_Type) return Display_Type;