'check_efer' uses 'do_not_nx'. Hotpluged CPU could wrongly disable NX.

Signed-off-by: Shaohua Li<shaohua.li@intel.com>
Signed-off-by: NAndi Kleen <ak@suse.de>
Signed-off-by: NLinus Torvalds <torvalds@osdl.org>