dt-bindings: pinctrl: Add gpio bindings for Actions S900 SoC

Add gpio bindings for Actions Semi S900 SoC.

Signed-off-by: Manivannan Sadhasivam <manivannan.sadhasivam@linaro.org>
Reviewed-by: Rob Herring <robh@kernel.org>
Signed-off-by: Linus Walleij <linus.walleij@linaro.org>