soc/intel/skylake: Generate ACPI RMRR table

An ACPI RMRR table is requried for IOMMU to work properly with an
iGPU (without using passthrough mode), so create one along with the
DRHD DMAR table if the iGPU is present and enabled.

Test: build/boot google/chell and purism/librem13v2 with kernel
parameter 'intel_iommu=on' but without 'iommu=pt;' observe integrated
graphics functional without corruption.

Change-Id: I202fb3eb8618f99d41f3d1c5bbb83b2ec982aca4
Signed-off-by: Matt DeVillier <matt.devillier@gmail.com>
Reviewed-on: https://review.coreboot.org/27270
Tested-by: build bot (Jenkins) <no-reply@coreboot.org>
Reviewed-by: Nico Huber <nico.h@gmx.de>
Reviewed-by: Youness Alaoui <snifikino@gmail.com>
3 files changed