Fix broken _DIS and _SRS methods in ACPI AML irq routing.

Fix broken _DIS and _SRS methods in ACPI AML irq routing.

The RefOf() operator doesn't do what was expected (at least on Linux)
- issuing "Store(1, RefOf(PRQ0))" doesn't write to the PRQ0 Field
defined on the OperationRegion.  Instead, it seems to redefine PRQ0 to
be an integer.

Fix this by defining the _DIS and _SRS methods as pre-processor
macros.  This way the RefOf() operator isn't needed.