gpio: pca9570: Add DT bindings for NXP PCA9571

This patch adds device tree bindings for the NXP PCA9571,
a 8-bit I2C GPIO expander.
Signed-off-by: NLucas Stach <l.stach@pengutronix.de>
Acked-by: NKrzysztof Kozlowski <krzysztof.kozlowski@linaro.org>
Signed-off-by: NBartosz Golaszewski <brgl@bgdev.pl>

Documentation/devicetree/bindings/gpio/gpio-pca9570.yaml

@@ -13,6 +13,7 @@ properties:
   compatible:
     enum:
       - nxp,pca9570
+      - nxp,pca9571
 
   reg:
     maxItems: 1