mb/lenovo/t400: Correct display port list for R500 variant

The second digital display connector is unused, but strapped as if it
were used.

Versions with a discrete GPU seem to use PM45 (i.e. no IGD), so we can
ignore these.

Based on schematics only, not tested.

Change-Id: Ibb47fdeef2adb9c574b7f3ec8e2b1d61d28f21da
Signed-off-by: Nico Huber <nico.h@gmx.de>
Reviewed-on: https://review.coreboot.org/c/coreboot/+/38574
Tested-by: build bot (Jenkins) <no-reply@coreboot.org>
Reviewed-by: Angel Pons <th3fanbus@gmail.com>
Reviewed-by: Kyösti Mälkki <kyosti.malkki@gmail.com>
Reviewed-by: Arthur Heymans <arthur@aheymans.xyz>

src/mainboard/lenovo/t400/variants/r500/gma-mainboard.ads

@@ -23,7 +23,6 @@ private package GMA.Mainboard is
    ports : constant Port_List :=
      (DP1,
       HDMI1,
-      HDMI2,
       Analog,
       Internal,
       others => Disabled);