dt-bindings: clk: hisilicon: Add bindings for Hi3670 clk

Add devicetree bindings for HiSilicon Hi3670 clock controller.

Signed-off-by: Manivannan Sadhasivam <manivannan.sadhasivam@linaro.org>
Reviewed-by: Rob Herring <robh@kernel.org>
Signed-off-by: Stephen Boyd <sboyd@kernel.org>