dt-bindings: thermal: loongson,ls2k-thermal: Add Loongson-2K0500 compatible

The thermal on the Loongson-2K0500 shares the design with the
Loongson-2K1000. Define corresponding compatible string, having the
loongson,ls2k1000-thermal as a fallback.

Signed-off-by: Binbin Zhou <zhoubinbin@loongson.cn>
Acked-by: Rob Herring <robh@kernel.org>
Acked-by: Huacai Chen <chenhuacai@loongson.cn>
Signed-off-by: Daniel Lezcano <daniel.lezcano@linaro.org>
Link: https://lore.kernel.org/r/26524a63abd2d032e4c45efe6ce3fedb46841768.1713837379.git.zhoubinbin@loongson.cn