sched: Unify the ->cpus_allowed mask copy

Currently every sched_class::set_cpus_allowed() implementation has to
copy the cpumask into task_struct::cpus_allowed, this is pointless,
put this copy in the generic code.

Signed-off-by: Peter Zijlstra <a.p.zijlstra@chello.nl>
Acked-by: Thomas Gleixner <tglx@linutronix.de>
Link: http://lkml.kernel.org/n/tip-jhl5s9fckd9ptw1fzbqqlrd3@git.kernel.org
Signed-off-by: Ingo Molnar <mingo@elte.hu>

kernel/sched_rt.c

@@ -1608,9 +1608,6 @@ static void set_cpus_allowed_rt(struct task_struct *p,
 
 		update_rt_migration(&rq->rt);
 	}
-
-	cpumask_copy(&p->cpus_allowed, new_mask);
-	p->rt.nr_cpus_allowed = weight;
 }
 
 /* Assumes rq->lock is held */