dt-bindings: clock: add loongson-2 clock include file

This file defines all Loongson-2 SoC clock indexes, it should be
included in the device tree in which there's device using the
clocks.

Signed-off-by: Yinbo Zhu <zhuyinbo@loongson.cn>
Acked-by: Krzysztof Kozlowski <krzysztof.kozlowski@linaro.org>
Link: https://lore.kernel.org/r/20221129034157.15036-1-zhuyinbo@loongson.cn


Signed-off-by: Stephen Boyd <sboyd@kernel.org>