reset: add DT bindings header for Gemini reset controller

This adds the DT binding macros used by the reset controller.

Acked-by: Rob Herring <robh@kernel.org>
Signed-off-by: Linus Walleij <linus.walleij@linaro.org>
Signed-off-by: Philipp Zabel <p.zabel@pengutronix.de>