KVM: selftests: Verify SNP VMs are rejected from migration and mirroring

KVM: selftests: Verify SNP VMs are rejected from migration and mirroring

Migration and mirroring of SEV-SNP VMs are not supported yet.

Add two selftests that verify KVM rejects intra-host migration and
mirroring when the source VM is an SNP VM, so the restriction stays enforced
until proper SNP state transfer is implemented.

Signed-off-by: Atish Patra <atishp@meta.com>
Link: https://patch.msgid.link/20260602-sev_snp_fixes-v3-2-24bfd3ae047c@meta.com
Signed-off-by: Sean Christopherson <seanjc@google.com>