Yep, mmap is definitely a possibility here, though finding out where everything is is a bit of a pain (Derek Molloy's device tree charts really help here: http://derekmolloy.ie/beaglebone/beaglebone-gpio-programming...).

An example of LED toggling via mmap on the Beaglebone is here: https://github.com/MarkAYoder/BeagleBoard-exercises/blob/mas... (and the associated tutorial: http://elinux.org/EBC_Exercise_11b_gpio_via_mmap)