Short version:
"gpioctl {53|54|55|56} {0|1}"
The user LEDs on Beaglebone and Beaglebone Black are connected to GPIO1_21 through GPIO1_24 of AM335x according to Service Reference Manuals(*1). GPIO pins of AM335x are grouped as four 32-channel groups (*2), group 0~3 and pin 0~31. FreeBSD represents all pins as flat addressing 0~127. So the corresponding pin number of the first LED for gpioctl is (32+21) = 53.
(*1): Beaglebone & Beaglebone Black Service Reference Manual are available at http://circuitco.com/
(*2): According to AM335x manual, TI doc# SPRS717F, available at http://www.ti.com/product/am3359.
