Decouple IRQ issues (MSI, i386, x86_64, ia64)

The following patchset is against 2.6.17-rc6-mm2.
It was the only easy place I could get everyones work who has been touching relevant code.

The primary aim of this patch is to remove maintenances problems caused by the irq infrastructure. The two big issues I address are an artificially small cap on the number of irqs, and that MSI assumes vector == irq. My primary focus is on x86_64 but I have touched other architectures where necessary to keep them from breaking.

- To increase the number of irqs I modify the code to look at the (cpu, vector) pair instead of just looking at the vector.

With a large number of irqs available systems with a large irq count no longer need to compress their irq numbers to fit. Removing a lot of brittle special cases.

For acpi guys the result is that irq == gsi.

- Addressing the fact that MSI assumes irq == vector takes a few more patches. But suffice it to say when I am done none of the generic irq code even knows what a vector is.

In quick testing on a large Unisys x86_64 machine we stumbled over at least one driver that assumed that NR_IRQS could always fit into an 8 bit number. This driver is clearly buggy today. But this has become a class of bugs that it is now much easier to hit.

I've done my best but if this patchset wasn't perfect it won't surprise me. But I'm pretty certain I have succeeded in decoupling any fixes should be small and well contained.

Eric