source count pointers at them so that intr_execute_handlers() won't
choke when it tries to handle an unregisterd ATPIC interrupt source.
- Install the low-level ATPIC interrupt handlers when we first program the
ATPIC in atpic_startup() rather than at SI_SUB_INTR. This is only
necessary to work around buggy code that enables interrupts too early
in the boot process (namely, the vm86 code).
Approved by: re (rwatson)