Add trigger command to gpio.c

[JakeZw]

To synchronized the MCC172 DAQ Hats, a trigger signal is required. If GPIO 23 is wired directly to the trigger input of the MCC172 then a short duration pulse on GPIO 23 can be used as the trigger.

My request is to add a function to gpio.c that will output a short duration 3.3 volt signal to GPIO 23 to allow software to trigger the MCC172.