kvm: vmx: keep constant definition format consistent

Keep all constants using lowercase "x".

Signed-off-by: Peng Hao <flyingpeng@tencent.com>
Message-Id: <CAPm50aKnctFL_7fZ-eqrz-QGnjW2+DTyDDrhxi7UZVO3HjD8UA@mail.gmail.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>