sched: clean up SCHED_CPUMASK_ALLOC

Impact: cleanup

The #if/#endif is ugly. Change SCHED_CPUMASK_ALLOC and
SCHED_CPUMASK_FREE to static inline functions.

Signed-off-by: Li Zefan <lizf@cn.fujitsu.com>
Acked-by: Peter Zijlstra <a.p.zijlstra@chello.nl>
Signed-off-by: Ingo Molnar <mingo@elte.hu>