x86: setup_smep needs to be __cpuinit

The setup_smep function gets calle at resume time too, and is thus not a
pure __init function.  When marked as __init, it gets thrown out after
the kernel has initialized, and when the kernel is suspended and
resumed, the code will no longer be around, and we'll get a nice "kernel
tried to execute NX-protected page" oops because the page is no longer
marked executable.

Reported-and-tested-by: Parag Warudkar <parag.lkml@gmail.com>
Cc: Fenghua Yu <fenghua.yu@intel.com>
Cc: "H. Peter Anvin" <hpa@linux.intel.com>
Cc: Ingo Molnar <mingo@elte.hu>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>