LoongArch: KVM: Implement VM related functions

Implement LoongArch VM operations: Init and destroy vm interface,
allocating memory page to save the vm pgd when init vm. Implement
vm check extension, such as getting vcpu number info, memory slots
info, and fpu info. And implement vm status description.

Reviewed-by: Bibo Mao <maobibo@loongson.cn>
Tested-by: Huacai Chen <chenhuacai@loongson.cn>
Signed-off-by: Tianrui Zhao <zhaotianrui@loongson.cn>
Signed-off-by: Huacai Chen <chenhuacai@loongson.cn>