dt-bindings: Add Oxford Semiconductor OXNAS pinctrl and gpio bindings

Add pinctrl and gpio DT bindings for Oxford Semiconductor OXNAS SoC Family.
This version supports the ARM926EJ-S based OX810SE SoC with 34 IO pins.

Signed-off-by: Neil Armstrong <narmstrong@baylibre.com>
Acked-by: Rob Herring <robh@kernel.org>
Signed-off-by: Linus Walleij <linus.walleij@linaro.org>