gpiolib: Introduce acpi_gpio_dev_init() and call it from core

In the ACPI case we may use the firmware node in the similar way
as it's done for OF case. We may use that fwnode for other purposes
in the future.

Signed-off-by: Andy Shevchenko <andriy.shevchenko@linux.intel.com>
Reviewed-by: Linus Walleij <linus.walleij@linaro.org>
Signed-off-by: Bartosz Golaszewski <bgolaszewski@baylibre.com>