clk: add DT bindings header for Gemini clock controller

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

Acked-by: Rob Herring <robh@kernel.org>
Signed-off-by: Linus Walleij <linus.walleij@linaro.org>
Signed-off-by: Stephen Boyd <sboyd@codeaurora.org>