KVM: VMX: enable invlpg exiting if EPT is disabled

Manually disabling EPT via module option fails to re-enable INVLPG
exiting.

Reported-by: Gleb Natapov <gleb@redhat.com>
Signed-off-by: Marcelo Tosatti <mtosatti@redhat.com>
Signed-off-by: Avi Kivity <avi@qumranet.com>