Fix isa_wrongintr. The APIC vector was being directly assigned to a C

Fix isa_wrongintr.  The APIC vector was being directly assigned to a C
function, resulting in register corruption and other nasties.  Generate
a set of assembly functions to handle wrong-interrupt assignments.  For
now we just EOI the apic and iret.

This bug could cause an SMP box to crash on boot if a spurious IRQ #0
interrupt occurs while it is testing for 8254 interrupt delivery.