dt-bindings: gpio: rockchip: add gpio-ranges

Allow usage of gpio-ranges with the rockchip gpio controller. The driver
already had support for this since it has been added to the mainline kernel
in the first place.

Acked-by: Rob Herring <robh@kernel.org>
Signed-off-by: Sebastian Reichel <sebastian.reichel@collabora.com>
Reviewed-by: Heiko Stuebner <heiko@sntech.de>
Reviewed-by: Linus Walleij <linus.walleij@linaro.org>
Signed-off-by: Bartosz Golaszewski <brgl@bgdev.pl>