ACPI: SCI interrupt source override

The Linux group at Stratus Technologies has come across an issue with SCI
routing under ACPI.  We were bitten by this when we made an x86_64 platform
whose BIOS provides an Interrupt Source Override for the SCI itself.
Apparently the override has no effect for the System Control Interrupt, and
this appears to be because of the way the SCI is setup in the ACPI code.
It does not handle the case where busirq != gsi.

The code that sets up the SCI routing assumes that bus irq == global irq.
So there is simply no provision for telling it otherwise.  The attached
patch provides this mechanism.

This patch provided by David Bulkow, was tested on an i386 platform, which
does not use the SCI override, and also on an x86_64 platform which does
use an override.

Signed-off-by: David Bulkow <david.bulkow@stratus.com>
Cc: Andi Kleen <ak@muc.de>
Signed-off-by: Andrew Morton <akpm@osdl.org>
Signed-off-by: Len Brown <len.brown@intel.com>