clk: rockchip: add dt-binding header for rk3399

Add the dt-bindings header for the rk3399, that gets shared between
the clock controller and the clock references in the dts.
Signed-off-by: NXing Zheng <zhengxing@rock-chips.com>
Signed-off-by: NJianqun Xu <jay.xu@rock-chips.com>
Acked-by: NRob Herring <robh@kernel.org>
Signed-off-by: NHeiko Stuebner <heiko@sntech.de>