sched: Move sched_domains_numa_masks_clear() to DOWN_PREPARE

This is the last operation on the cpu before vanishing. No point in calling
that on CPU_DEAD.

Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Acked-by: Peter Zijlstra <peterz@infradead.org>
Cc: rt@linutronix.de
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>