gpiolib: Add gpiochip_set_data() helper

There are too many 'data' parameters here and there.

For the better maintenance keep access GPIO device data
via getter and setter.

Signed-off-by: Andy Shevchenko <andriy.shevchenko@linux.intel.com>
Signed-off-by: Bartosz Golaszewski <bartosz.golaszewski@linaro.org>