gma panel: Introduce `Panel_Control` type

For now, `Panel_Control` only distinguishes `Panel_1` from `No_Panel`,
i.e. if a port has a panel attached or not. To ease future addition of
support for more than one panel, we already add loops and arrays around
it, though.

With the information, if a port has a panel attached, in `Port_Config`,
we can pass that on into Panel.* procedures and let those decide what
to do (e.g. do nothing if no panel is attached).

Change-Id: I83864bc86b48f65d9ba43e083b805ca09497cbb0
Signed-off-by: Nico Huber <nico.huber@secunet.com>
Reviewed-on: https://review.coreboot.org/c/libgfxinit/+/38243
Tested-by: Nico Huber <nico.h@gmx.de>
Reviewed-by: Angel Pons <th3fanbus@gmail.com>
diff --git a/common/hw-gfx-gma-connector_info.adb b/common/hw-gfx-gma-connector_info.adb
index 3ce807e..dcbed2e 100644
--- a/common/hw-gfx-gma-connector_info.adb
+++ b/common/hw-gfx-gma-connector_info.adb
@@ -38,12 +38,10 @@
       pragma Debug (Debug.Put_Line (GNAT.Source_Info.Enclosing_Entity));
 
       if Port_Cfg.Display = DP then
-         if Port_Cfg.Port = DIGI_A then
-            if GMA.Config.Use_PP_VDD_Override then
-               Panel.VDD_Override;
-            else
-               Panel.On;
-            end if;
+         if GMA.Config.Use_PP_VDD_Override then
+            Panel.VDD_Override (Port_Cfg.Panel);
+         else
+            Panel.On (Port_Cfg.Panel);
          end if;
 
          DP_Info.Read_Caps