gpio: dwapb: Switch to use fwnode instead of of_node

GPIO library now accepts fwnode as a firmware node, so
switch the driver to use it and hence rectify the ACPI
case which uses software nodes.

Note, in this case it's rather logical fix that doesn't
affect functionality, thus no backporting required.

Signed-off-by: Andy Shevchenko <andriy.shevchenko@linux.intel.com>
Acked-by: Serge Semin <fancer.lancer@gmail.com>
Signed-off-by: Bartosz Golaszewski <brgl@bgdev.pl>