KVM: VMX: do not check bit 12 of EPT violation exit qualification when undefined

Bit 12 is undefined in any of the following cases:
- If the "NMI exiting" VM-execution control is 1 and the "virtual NMIs"
  VM-execution control is 0.
- If the VM exit sets the valid bit in the IDT-vectoring information field

Signed-off-by: Gleb Natapov <gleb@redhat.com>
[Add parentheses around & within && - Paolo]
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>