KVM: SEV: Do not allow intra-host migration/mirroring of SNP VMs

In the Linux kernel, the following vulnerability has been resolved: KVM: SEV: Do not allow intra-host migration/mirroring of SNP VMs The intra-host migration/mirroring feature is not fully implemented for SEV-SNP VMs. The proper migration requires additional SNP-specific state such as guest_req_mutex, guest_req_buf, and guest_resp_buf to be transferred or initialized on the destination. The SNP VM mirroring requires vmsa features to be copied as well otherwise ASID would be bound to SNP range while VM is detected as a SEV VM. Reject SNP source VMs in migration/mirroring until proper SNP state transfer is implemented. [sean: let lines poke past 80 chars, tag for stable]