ACPI: Altix: ACPI _PRT support

Provide ACPI _PRT support for SN Altix systems.

The SN Altix platform does not conform to the
IOSAPIC IRQ routing model, so a new acpi_irq_model
(ACPI_IRQ_MODEL_PLATFORM) has been defined. The SN
platform specific code sets acpi_irq_model to
this new value, and keys off of it in acpi_register_gsi()
to avoid the iosapic code path.

Signed-off-by: John Keller <jpk@sgi.com>
Signed-off-by: Len Brown <len.brown@intel.com>
diff --git a/include/linux/acpi.h b/include/linux/acpi.h
index 2b0c955..91f1f23 100644
--- a/include/linux/acpi.h
+++ b/include/linux/acpi.h
@@ -47,6 +47,7 @@
 	ACPI_IRQ_MODEL_PIC = 0,
 	ACPI_IRQ_MODEL_IOAPIC,
 	ACPI_IRQ_MODEL_IOSAPIC,
+	ACPI_IRQ_MODEL_PLATFORM,
 	ACPI_IRQ_MODEL_COUNT
 };