mb/lenovo/t430s: Enable libgfxinit

Tested on T430s with an external screen connected to every one of the
DP ports (miniDP on mainboard, two DP ports on dock), the GRUB payload
can display on both the external screen and the internal LVDS screen.

This is a copy-paste of I8f270d55 "mb/lenovo/x230: Enable libgfxinit".

Change-Id: Ifb1471ecb18927c30c61c64011cbb0e20a465558
Signed-off-by: Bill XIE <persmule@gmail.com>
Reviewed-on: https://review.coreboot.org/21070
Tested-by: build bot (Jenkins) <no-reply@coreboot.org>
Reviewed-by: Arthur Heymans <arthur@aheymans.xyz>
3 files changed