Make `InterruptModel` non_exhaustive

This makes it not-a-breaking-change to add new interrupt models in the
future, and isn't a big onus on users as they'll likely want a wildcard
pattern anyway, as not all interrupt models will be supported on their
architecture anyway.

acpi/src/interrupt.rs

@@ -75,6 +75,7 @@ pub struct Apic {
 }
 
 #[derive(Debug)]
+#[non_exhaustive]
 pub enum InterruptModel {
     /// This model is only chosen when a newer one can not be found and the system supports the
     /// legacy dual-8259 PIC.