runtime/interrupt: add cross-chip disable/restore interrupt support

This should cover all supported baremetal targets.

src/runtime/interrupt/interrupt_gameboyadvance.go

@@ -34,3 +34,32 @@ func handleInterrupt() {
 // appropriate interrupt handler for the given interrupt ID.
 //go:linkname callInterruptHandler runtime.callInterruptHandler
 func callInterruptHandler(id int)
+
+// State represents the previous global interrupt state.
+type State uint8
+
+// Disable disables all interrupts and returns the previous interrupt state. It
+// can be used in a critical section like this:
+//
+//     state := interrupt.Disable()
+//     // critical section
+//     interrupt.Restore(state)
+//
+// Critical sections can be nested. Make sure to call Restore in the same order
+// as you called Disable (this happens naturally with the pattern above).
+func Disable() (state State) {
+	// Save the previous interrupt state.
+	state = State(regInterruptMasterEnable.Get())
+	// Disable all interrupts.
+	regInterruptMasterEnable.Set(0)
+	return
+}
+
+// Restore restores interrupts to what they were before. Give the previous state
+// returned by Disable as a parameter. If interrupts were disabled before
+// calling Disable, this will not re-enable interrupts, allowing for nested
+// cricital sections.
+func Restore(state State) {
+	// Restore interrupts to the previous state.
+	regInterruptMasterEnable.Set(uint16(state))
+}