KVM: selftests: Add a basic SEV smoke test

KVM: selftests: Add a basic SEV smoke test

Add a basic smoke test for SEV guests to verify that KVM can launch an
SEV guest and run a few instructions without exploding.  To verify that
SEV is indeed enabled, assert that SEV is reported as enabled in
MSR_AMD64_SEV, a.k.a. SEV_STATUS, which cannot be intercepted by KVM
(architecturally enforced).

Cc: Paolo Bonzini <pbonzini@redhat.com>
Cc: Sean Christopherson <seanjc@google.com>
Cc: Vishal Annapurve <vannapurve@google.com>
Cc: Ackerly Tng <ackerleytng@google.com>
cc: Andrew Jones <andrew.jones@linux.dev>
Cc: Tom Lendacky <thomas.lendacky@amd.com>
Cc: Michael Roth <michael.roth@amd.com>
Suggested-by: Michael Roth <michael.roth@amd.com>
Tested-by: Carlos Bilbao <carlos.bilbao@amd.com>
Signed-off-by: Peter Gonda <pgonda@google.com>
[sean: rename to "sev_smoke_test"]
Link: https://lore.kernel.org/r/20240223004258.3104051-11-seanjc@google.com
Signed-off-by: Sean Christopherson <seanjc@google.com>