gpio: dwapb: convert device node to fwnode

This patch converts device node to fwnode for dwapb driver, so
as to provide a unified fwnode for DT and ACPI bindings.

Tested-by: Alan Tull <delicious.quinoa@gmail.com>
Acked-by: Andy Shevchenko <andy.shevchenko@gmail.com>
Signed-off-by: Jiang Qiu <qiujiang@huawei.com>
Signed-off-by: Linus Walleij <linus.walleij@linaro.org>