x86, acpi/irq: Teach acpi_get_override_irq to take a gsi not an isa_irq

In perverse acpi implementations the isa irqs are not identity mapped
to the first 16 gsi.  Furthermore at least the extended interrupt
resource capability may return gsi's and not isa irqs.  So since
what we get from acpi is a gsi teach acpi_get_overrride_irq to
operate on a gsi instead of an isa_irq.

Signed-off-by: Eric W. Biederman <ebiederm@xmission.com>
LKML-Reference: <1269936436-7039-2-git-send-email-ebiederm@xmission.com>
Signed-off-by: H. Peter Anvin <hpa@zytor.com>