dt-bindings: gpio: pca953x: add nxp,pcal9535

The NXP PCAL9535 is an extended variant of the PCA9535.

Signed-off-by: Jan Kiszka <jan.kiszka@siemens.com>
Reviewed-by: Andy Shevchenko <andy.shevchenko@gmail.com>
Signed-off-by: Bartosz Golaszewski <bgolaszewski@baylibre.com>