SMAP: added stac() and clac() to cpufunc.h

Signed-off-by: Oliver Pinter <oliver.pntr@gmail.com>
SMAP: added CR4_SMAP to sys/x86/include/specialreg.h

Signed-off-by: Oliver Pinter <oliver.pntr@gmail.com>
SMAP: updated PSL_AC's comment in sys/x86/include/psl.h

Signed-off-by: Oliver Pinter <oliver.pntr@gmail.com>