s390/nohz: use a per-cpu flag for arch_needs_cpu

Move the nohz_delay bit from the s390_idle data structure to the
per-cpu flags. Clear the nohz delay flag in __cpu_disable and
remove the cpu hotplug notifier that used to do this.

Signed-off-by: Martin Schwidefsky <schwidefsky@de.ibm.com>

drivers/s390/cio/airq.c

@@ -87,7 +87,7 @@ static irqreturn_t do_airq_interrupt(int irq, void *dummy)
 	struct airq_struct *airq;
 	struct hlist_head *head;
 
-	__this_cpu_write(s390_idle.nohz_delay, 1);
+	set_cpu_flag(CIF_NOHZ_DELAY);
 	tpi_info = (struct tpi_info *) &get_irq_regs()->int_code;
 	head = &airq_lists[tpi_info->isc];
 	rcu_read_lock();