thermal/drivers/loongson2: Add Loongson-2K2000 support

The Loongson-2K2000 and Loongson-2K1000 have similar thermal sensors,
except that the temperature is read differently.

In particular, the temperature output registers of the Loongson-2K2000
are defined in the chip configuration domain and are read in a different
way.

Signed-off-by: Binbin Zhou <zhoubinbin@loongson.cn>
Acked-by: Huacai Chen <chenhuacai@loongson.cn>
Signed-off-by: Daniel Lezcano <daniel.lezcano@linaro.org>
Link: https://lore.kernel.org/r/fdbfdcc3231a36a4ee0bcf1377ddcbd6f8c944b5.1713837379.git.zhoubinbin@loongson.cn