dt-bindings: pinctrl: Add X1500 bindings.

Add the pinctrl bindings for the X1500 Soc from Ingenic.
Signed-off-by: Zhou Yanjie <zhouyanjie@zoho.com>
Link: https://lore.kernel.org/r/1563076436-5338-6-git-send-email-zhouyanjie@zoho.comSigned-off-by: Linus Walleij <linus.walleij@linaro.org>

Documentation/devicetree/bindings/pinctrl/ingenic,pinctrl.txt

@@ -27,6 +27,7 @@ Required properties:
     - "ingenic,jz4780-pinctrl"
     - "ingenic,x1000-pinctrl"
     - "ingenic,x1000e-pinctrl"
+    - "ingenic,x1500-pinctrl"
  - reg: Address range of the pinctrl registers.