gma: Refactor Port_Config derivation

Mostly renaming and some type tightening. Move the call to
Configure_FDI_Link() into Fill_Port_Config() as it's part of the
Port_Config.

Also start to document some procedures. The whole high-level con-
figuration is driven by non-obvious software-design choices, and
thus isn't self-explanatory even if you know the hardware.

Change-Id: Ib6a0893333e9359776140ed9de110f54cf36f6e5
Signed-off-by: Nico Huber <nico.h@gmx.de>
Reviewed-on: https://review.coreboot.org/17756
Reviewed-by: Adrian-Ken Rueegsegger <ken@codelabs.ch>
diff --git a/common/haswell_shared/hw-gfx-gma-connectors.adb b/common/haswell_shared/hw-gfx-gma-connectors.adb
index b21ca9a..7e8f133 100644
--- a/common/haswell_shared/hw-gfx-gma-connectors.adb
+++ b/common/haswell_shared/hw-gfx-gma-connectors.adb
@@ -86,7 +86,7 @@
       for Port in Digital_Port range DIGI_A .. DIGI_D loop
          DDI.Off (Port);
       end loop;
-      if Config.FDI_Port (DIGI_E) then
+      if Config.Is_FDI_Port (Analog) then
          DDI.Off (DIGI_E);
       end if;
    end Post_All_Off;