gpio: reference count the gpio device for each desc
Every time a descriptor is retrieved from the gpiolib, we issue
module_get() to reference count the module supplying the GPIOs.
We also need to call device_get() and device_put() as we also
reference the backing gpio_device when doing this.
Since the sysfs GPIO interface is using gpiod_get() this will
also reference count the sysfs requests until all GPIOs are
unexported.