selftests: kvm: fix smm test on SVM

KVM_CAP_NESTED_STATE is now supported for AMD too but smm test acts like
it is still Intel only.

Signed-off-by: Vitaly Kuznetsov <vkuznets@redhat.com>
Message-Id: <20200529130407.57176-2-vkuznets@redhat.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>