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

This should cover all supported baremetal targets.

src/runtime/interrupt/interrupt_cortexm.go

@@ -21,3 +21,27 @@ func (irq Interrupt) Enable() {
 func (irq Interrupt) SetPriority(priority uint8) {
 	arm.SetPriority(uint32(irq.num), uint32(priority))
 }
+
+// State represents the previous global interrupt state.
+type State uintptr
+
+// 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) {
+	return State(arm.DisableInterrupts())
+}
+
+// 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) {
+	arm.EnableInterrupts(uintptr(state))
+}