interrupt threads to run with it always >= 1, so that malloc can
detect M_WAITOK from "interrupt" context. This is also necessary
in order to context switch from sched_ithd() directly.
Reviewed By: peter
not work on any real hardware (or fully work on any simulator). Much more
needs to happen before this is actually functional but its nice to see
the FreeBSD copyright message appear in the ia64 simulator.