dt-bindings: clock: add loongson-2 clock

Add the Loongson-2 clock binding with DT schema format using
json-schema.

Signed-off-by: Yinbo Zhu <zhuyinbo@loongson.cn>
Reviewed-by: Krzysztof Kozlowski <krzysztof.kozlowski@linaro.org>
Link: https://lore.kernel.org/r/20221129034157.15036-4-zhuyinbo@loongson.cn


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