pinctrl: microchip-sgpio: Switch to use fwnode instead of of_node

GPIO library now accepts fwnode as a firmware node, so
switch the driver to use it.

Signed-off-by: Andy Shevchenko <andriy.shevchenko@linux.intel.com>
Link: https://lore.kernel.org/r/20220503151517.59115-1-andriy.shevchenko@linux.intel.com


Signed-off-by: Linus Walleij <linus.walleij@linaro.org>