machine/rp2040: add machine.Sleep api

[soypat]

@aykevl @deadprogram @ysoldak PTAL! This is a new API addition to machine package. Provides a way to set processor in a low power state until an interrupt is triggered via a PinEvent.

// Sets raspberry pico in dormant state until interrupt event is triggered
// usage:
//  err := machine.Sleep(interruptPin, machine.PinRising)
// Above code will cause program to sleep until a high level signal
// is found on interruptPin. Be sure to configure pin as input beforehand.
// Taken from https://github.com/raspberrypi/pico-extras/ -> pico/sleep.h
func Sleep(pin Pin, change PinChange) error {