KVM: SVM: Rename SEV implemenations to conform to kvm_x86_ops hooks

Rename svm_vm_copy_asid_from() and svm_vm_migrate_from() to conform to
the names used by kvm_x86_ops, and opportunistically use "sev" instead of
"svm" to more precisely identify the role of the hooks.

svm_vm_copy_asid_from() in particular was poorly named as the function
does much more than simply copy the ASID.

No functional change intended.

Signed-off-by: Sean Christopherson <seanjc@google.com>
Message-Id: <20220128005208.4008533-21-seanjc@google.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>