CONFIG_OF_GPIO (not configurable)

modulename: gpio.ko

and/or

gpiolib-of.ko

configname: CONFIG_OF_GPIO

Linux Kernel Configuration
└─>Device Drivers
└─>Device Tree and Open Firmware support
└─>OF_GPIO
In linux kernel since version 2.6.26 (release Date: 2008-07-13)  
OpenFirmware GPIO accessors

source code:
drivers/of/gpio.c