mb/lenovo/t420: Enable libgfxinit

In the single GPU configuration, the T420 has an LVDS port, one DP++
and one VGA port connected to the IGD. Docking solutions feature up to
two additional DP/DVI-D ports, also directly connected to the IGD.
This makes the list of ports to probe pretty long (takes about 70ms
if nothing but LVDS is connected). We could save about 20~30ms if we'd
limit the ports in case we are not docked or have a discrete GPU.

Change-Id: I8e02c8003ff745d05ee272c59377174847f5219c
Signed-off-by: Nico Huber <nico.h@gmx.de>
Reviewed-on: https://review.coreboot.org/19378
Tested-by: build bot (Jenkins)
Reviewed-by: Arthur Heymans <arthur@aheymans.xyz>

src/mainboard/lenovo/t420/Kconfig

@@ -20,6 +20,8 @@ config BOARD_SPECIFIC_OPTIONS # dummy
 	select ENABLE_VMX
 	select DRIVERS_RICOH_RCE822
 	select MAINBOARD_HAS_LPC_TPM
+	select MAINBOARD_HAS_LIBGFXINIT
+	select GFX_GMA_INTERNAL_IS_LVDS
 
 	# Workaround for EC/KBC IRQ1.
 	select SERIRQ_CONTINUOUS_MODE

src/mainboard/lenovo/t420/Makefile.inc

@@ -15,3 +15,5 @@
 
 smm-$(CONFIG_HAVE_SMI_HANDLER) += smihandler.c
 romstage-y += gpio.c
+
+ramstage-$(CONFIG_MAINBOARD_USE_LIBGFXINIT) += gma-mainboard.ads

src/mainboard/lenovo/t420/gma-mainboard.ads

@@ -0,0 +1,20 @@
+with HW.GFX.GMA;
+with HW.GFX.GMA.Display_Probing;
+
+use HW.GFX.GMA;
+use HW.GFX.GMA.Display_Probing;
+
+private package GMA.Mainboard is
+
+   ports : constant Port_List :=
+     (DP1,
+      DP2,
+      DP3,
+      HDMI1,
+      HDMI2,
+      HDMI3,
+      Analog,
+      Internal,
+      others => Disabled);
+
+end GMA.Mainboard;