Use LED subsystem's `/sys/class/leds/<led>/hw_pattern` to trigger m4 LED blinking
following up on yesterdays discussion on the interface between m4 core and linux kernel: we can make the led blinking part a relatively simple led driver on the linux side that fills in
set_pattern so the
pattern trigger can use
hw_pattern to set the actual pattern. We then just need the m4 side to handle that.