LoongArch: KVM: Add PCHPIC read and write functions

Add implementation of IPI interrupt controller's address space read and
write function simulation.

Implement interrupt injection interface under loongarch.

Signed-off-by: Tianrui Zhao <zhaotianrui@loongson.cn>
Signed-off-by: Xianglai Li <lixianglai@loongson.cn>
Signed-off-by: Huacai Chen <chenhuacai@loongson.cn>