dt-bindings: gpio: pca953x: document the nxp,pca6416

The NXP PCA6416 is a variant of the PCA GPIO expander, with 16 GPIOs.
Signed-off-by: Alexandre Belloni <alexandre.belloni@bootlin.com>
Signed-off-by: Linus Walleij <linus.walleij@linaro.org>

Documentation/devicetree/bindings/gpio/gpio-pca953x.txt

@@ -2,6 +2,7 @@
 
 Required properties:
  - compatible: Has to contain one of the following:
+	nxp,pca6416
 	nxp,pca9505
 	nxp,pca9534
 	nxp,pca9535