LoongArch: KVM: Implement kvm module related interface

Implement LoongArch kvm module init, module exit interface, using kvm
context to save the vpid info and vcpu world switch interface pointer.
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>