s390/smp: Make cpu notifier symetric

There is no reason to remove the sysfs cpu files when the CPU is dead, they
can be removed when the cpu is prepared to go down. Doing it at
DOWN_PREPARE allows us to convert it to a symetric hotplug state in the
next step.

Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Signed-off-by: Sebastian Andrzej Siewior <bigeasy@linutronix.de>
Acked-by: Heiko Carstens <heiko.carstens@de.ibm.com>
Cc: Martin Schwidefsky <schwidefsky@de.ibm.com>
Cc: linux-s390@vger.kernel.org
Cc: rt@linutronix.de
Link: http://lkml.kernel.org/r/20161104144140.lcee6kwmwlx37m7g@linutronix.de
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>

arch/s390/kernel/smp.c

@@ -1056,9 +1056,10 @@ static int smp_cpu_notify(struct notifier_block *self, unsigned long action,
 
 	switch (action & ~CPU_TASKS_FROZEN) {
 	case CPU_ONLINE:
+	case CPU_DOWN_FAILED:
 		err = sysfs_create_group(&s->kobj, &cpu_online_attr_group);
 		break;
-	case CPU_DEAD:
+	case CPU_DOWN_PREPARE:
 		sysfs_remove_group(&s->kobj, &cpu_online_attr_group);
 		break;
 	}