dt-bindings: arm: fsl-scu: Add imx8dxl pinctrl support

Update binding doc to support i.MX8DXL pinctrl.

Signed-off-by: Anson Huang <Anson.Huang@nxp.com>
Acked-by: Rob Herring <robh@kernel.org>
Link: https://lore.kernel.org/r/1585306559-13973-1-git-send-email-Anson.Huang@nxp.com


Signed-off-by: Linus Walleij <linus.walleij@linaro.org>