dt-bindings: soc: add loongson-2 chipid

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

Signed-off-by: Yinbo Zhu <zhuyinbo@loongson.cn>
Reviewed-by: Rob Herring <robh@kernel.org>
Link: https://lore.kernel.org/r/20221111054201.18528-2-zhuyinbo@loongson.cn

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Signed-off-by: Arnd Bergmann <arnd@arndb.de>