will disable the ACPI interpreter init, but not stop the OS from using
ACPI tables for finding CPUs and IOAPICs. Another problem is that if we
use the tables, but then the interpreter fails to init, we are in deep
trouble, because it is too late to revert to using MPS, but we cannot get
_PRT info without the interpreter.

This changeset doesn't fix the latter problem, but it does at least make
"acpi=off" actually do what it says, and not use the ACPI interpreter *or*
the tables.