This fixes the known problems of 2.1.80, and also makes the interrupt
routing by default look like it always used to look - everything goes
through the traditional external 8259A-compatible logic.
The code to handle IO-APIC interrupt routing is still there, but as no
interrupts are actually marked as io-apic interrupts you don't see it in
action yet. The advantage of this is that people who want to work on this
have a base that contains all the logic, and that we only need to figure
out how to reliably make all the IRQ routing decisions.
Linus