LoongArch: KVM: Implement kvm hardware enable, disable interface

Implement kvm hardware enable, disable interface, setting the
guest config register to enable virtualization features when called
the interface.

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>