dt-bindings: gpio: uniphier: add UniPhier GPIO binding

This GPIO controller is used on UniPhier SoC family.

The vendor specific property "socionext,interrupt-ranges" is for
specifying interrupt mapping to the parent interrupt controller
because the mapping is not contiguous. It works like "ranges",
but transforms "interrupts" instead of "reg".

Signed-off-by: Masahiro Yamada <yamada.masahiro@socionext.com>
Acked-by: Rob Herring <robh@kernel.org>
Signed-off-by: Linus Walleij <linus.walleij@linaro.org>