Skylake: Add support for Gfx PEIM (AKA GOP)

This patch implements the igd_opregion using the write_acpi_tables
mechanism to support GOP usage.

BRANCH=none
BUG=chrome-os-partner:44559
TEST=W/o GOP_SUPPORT in config, Built and boot on kunimitsu/glados.
W/ GOP_SUPPORT enabled, build and boot on kunimitsu/glados, but on
glados Dev screen can not be seen (OS display is fine).
CQ-DEPEND=CL:303539

Change-Id: I6f3c29c1b608eeaad8f2bf79d17394d49f8e412c
Signed-off-by: robbie zhang <robbie.zhang@intel.com>
Reviewed-on: https://chromium-review.googlesource.com/303387
Commit-Ready: Robbie Zhang <robbie.zhang@intel.com>
Tested-by: Robbie Zhang <robbie.zhang@intel.com>
Reviewed-by: Aaron Durbin <adurbin@chromium.org>
3 files changed