intel/skylake: Implement T states
T states are supported by the chipset, but coreboot doesn't provide the right setup. For that reason, we disable (or remove) the corresponding ACPI code for Skylake in https://review.coreboot.org/c/coreboot/+/38132
If T states are to be implemented, the ACPI code needs to be reinstated, too. See 38132 for details.