VT-d support needs to be specifically enabled by coreboot. VT-x can be enabled in software with a 'wrmsr' command, but VT-d requires iommu to be enabled from coreboot and DMAR ACPI tables to be created.
More information here : https://forums.puri.sm/t/clarification-on-librem-15-and-intel-me/1242/11?u=kakaroto
More specifically, here are resources linked in that forum thread that are related to this :
Note that gm45, and ivybridge has support for VT-d, it just needs to be ported to skylake.