KVM: selftests: Add SEV-ES shutdown test

Regression test for ae20eef5 ("KVM: SVM: Update SEV-ES shutdown intercepts
with more metadata"). Test confirms userspace is correctly indicated of
a guest shutdown not previous behavior of an EINVAL from KVM_RUN.

Cc: Paolo Bonzini <pbonzini@redhat.com>
Cc: Sean Christopherson <seanjc@google.com>
Cc: Alper Gun <alpergun@google.com>
Cc: Tom Lendacky <thomas.lendacky@amd.com>
Cc: Michael Roth <michael.roth@amd.com>
Cc: kvm@vger.kernel.org
Cc: linux-kselftest@vger.kernel.org
Signed-off-by: Peter Gonda <pgonda@google.com>
Tested-by: Pratik R. Sampat <pratikrajesh.sampat@amd.com>
Link: https://lore.kernel.org/r/20240709182936.146487-1-pgonda@google.com


[sean: clobber IDT to ensure #UD leads to SHUTDOWN]
Signed-off-by: Sean Christopherson <seanjc@google.com>