dt-bindings: gpio: pca953x: Document new supported chip pca9506

The previous patch added support for this chip. Add its name to the list
of allowed compatibles.

Signed-off-by: Uwe Kleine-König <u.kleine-koenig@pengutronix.de>
Reviewed-by: Linus Walleij <linus.walleij@linaro.org>
Signed-off-by: Bartosz Golaszewski <bgolaszewski@baylibre.com>

Documentation/devicetree/bindings/gpio/gpio-pca95xx.yaml

@@ -32,6 +32,7 @@ properties:
       - maxim,max7327
       - nxp,pca6416
       - nxp,pca9505
+      - nxp,pca9506
       - nxp,pca9534
       - nxp,pca9535
       - nxp,pca9536