System call entry functions sys_*() are never to be called from
general kernel code.  The fact that they aren't declared in header
files should have been a clue.  These functions also don't exist on
Alpha since it has sys_getxpid() instead.

Signed-off-by: Ben Hutchings <ben@decadent.org.uk>
Acked-by: Tetsuo Handa <penguin-kernel@I-love.SAKURA.ne.jp>
Signed-off-by: James Morris <jmorris@namei.org>