On the Boundary Devices kernel, and maybe others, you can use cat /sys/kernel/debug/gpio to get a list of the mapped gpios, their states, and name given when it was allocated. You can grep the kernel source for the name and find out what module grabbed it.
root@nitrogen6x:/opt# cat /sys/kernel/debug/gpio
GPIOs 0-31, platform/209c000.gpio, 209c000.gpio:
gpio-2 (flexcan-trx-stby ) out lo
gpio-17 (DISP_SCL ) out lo
GPIOs 32-63, platform/20a0000.gpio, 20a0000.gpio:
gpio-33 (sysfs ) out lo
gpio-35 (sysfs ) in hi
gpio-36 (sysfs ) in hi
gpio-37 (DISP_SDI ) out lo
gpio-38 (219c000.usdhc cd ) in hi
GPIOs 64-95, platform/20a4000.gpio, 20a4000.gpio:
gpio-83 (spi_imx ) out lo
gpio-86 (usb_otg_vbus ) out lo
GPIOs 96-127, platform/20a8000.gpio, 20a8000.gpio:
gpio-101 (sysfs ) in hi
gpio-116 (rst-gpios ) out lo
GPIOs 128-159, platform/20ac000.gpio, 20ac000.gpio:
GPIOs 160-191, platform/20b0000.gpio, 20b0000.gpio:
gpio-175 (wlan-en ) out lo
gpio-176 (bt_rfkill_reset ) out lo
GPIOs 192-223, platform/20b4000.gpio, 20b4000.gpio:
gpio-192 (2198000.usdhc cd ) in lo
gpio-204 (ehci_reset_gpio ) out lo
gpio-205 (sysfs ) in lo
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