KVM: nVMX: fail on invalid vmclear/vmptrld pointer

The spec mandates that if the vmptrld or vmclear
address is equal to the vmxon region pointer, the
instruction should fail with error "VMPTRLD with
VMXON pointer" or "VMCLEAR with VMXON pointer"

Signed-off-by: Bandan Das <bsd@redhat.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>