CONFIG_GPIO_REG (not configurable)

modulename: gpio-reg.ko

configname: CONFIG_GPIO_REG

Linux Kernel Configuration
└─>Device Drivers
└─>GPIO Support
└─>Memory mapped GPIO drivers
└─>GPIO_REG
In linux kernel since version 3.10 (release Date: 2013-06-30)  
A 32-bit single register GPIO fixed in/out implementation. This
can be used to represent any register as a set of GPIO signals.

source code:
drivers/gpio/gpio-reg.c