KVM: selftests: Don't probe KVM_CAP_HYPERV_ENLIGHTENED_VMCS when nested VMX is unsupported

KVM_CAP_HYPERV_ENLIGHTENED_VMCS will be reported as supported even when
nested VMX is not, fix evmcs_test/hyperv_cpuid tests to check for both.

Signed-off-by: Vitaly Kuznetsov <vkuznets@redhat.com>
Message-Id: <20200610135847.754289-3-vkuznets@redhat.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>