LoongArch: Update dts for Loongson-2K2000 to support ISA/LPC

Some Loongson-2K2000 platforms have ISA/LPC devices such as Super-IO,
define an ISA node in the dts file to avoid access error. Also adjust
the PCI io resource range to avoid confliction.

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