powerpc/83xx/mpc8349emitx: Get rid of of_node assignment

Let GPIO library to assign of_node from the parent device.
This allows to move GPIO library and drivers to use fwnode
APIs instead of being stuck with OF-only interfaces.

Signed-off-by: Andy Shevchenko <andriy.shevchenko@linux.intel.com>
Reviewed-by: Linus Walleij <linus.walleij@linaro.org>
Acked-by: Scott Wood <oss@buserror.net>
Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>
Link: https://lore.kernel.org/r/20220323174342.56187-1-andriy.shevchenko@linux.intel.com