LoongArch: dts: Add i2c clocks and clock-frequency properties to LS2K1000

Add missing clocks and clock-frequency properties to i2c nodes for LS2K1000.

Signed-off-by: Hongliang Wang <wanghongliang@loongson.cn>
Signed-off-by: Huacai Chen <chenhuacai@loongson.cn>

[ upstream commit: 0526f3ea9f5aeed79caf353679c15280af1539ec ]