soc/intel/skylake: Hook up libgfxinit

Also base the FSP/GOP related bail-out on the correct Kconfig option
to allow adding a VBT along with libgfxinit.

Most things should work, what doesn't is backlight control because
coreboot misses the settings (moved to FSP and need backporting).
Also, Kaby Lake is still unsupported.

TEST=Booted yet to be upstreamed Skylake-S port (Kontron/bSL6) both with
     text and linear framebuffer mode and viewed a FILO menu.

Change-Id: I79fbfed7732cf02d054530ea7ec0d34de32836ba
Signed-off-by: Nico Huber <nico.huber@secunet.com>
Reviewed-on: https://review.coreboot.org/20113
Tested-by: build bot (Jenkins) <no-reply@coreboot.org>
Reviewed-by: Subrata Banik <subrata.banik@intel.com>
1 file changed