The msi currently allocates irqs backwards.  First it allocates a platform
dependent routing value for an interrupt the ``vector'' and then it figures
out from the vector which irq you are on.

For ia64 this is fine.  For x86 and x86_64 this is complete nonsense and makes
an enourmous mess of the irq handling code and prevents some pretty
significant cleanups in the code for handling large numbers of irqs.

This patch refactors msi.c to work in terms of irqs and create_irq/destroy_irq
for dynamically managing irqs.

Hopefully this is finally a version of msi.c that is useful on more than just
x86 derivatives.

Signed-off-by: Eric W. Biederman <ebiederm@xmission.com>
Cc: Ingo Molnar <mingo@elte.hu>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: Benjamin Herrenschmidt <benh@kernel.crashing.org>
Cc: Rajesh Shah <rajesh.shah@intel.com>
Cc: Andi Kleen <ak@muc.de>
Cc: "Protasevich, Natalie" <Natalie.Protasevich@UNISYS.com>
Cc: "Luck, Tony" <tony.luck@intel.com>
Signed-off-by: Andrew Morton <akpm@osdl.org>
Signed-off-by: Linus Torvalds <torvalds@osdl.org>