[S390] Rename "idle_time" attribute to "idle_time_us".

Seems that people prefer to have the unit encoded in the attribute
name. Also makes parsing easier.

Now we have:

# cat /sys/devices/system/cpu/cpu0/idle_time_us
131473592

instead of

# cat /sys/devices/system/cpu/cpu0/idle_time
131473592 us

Cc: Arjan van de Ven <arjan@infradead.org>
Signed-off-by: Heiko Carstens <heiko.carstens@de.ibm.com>
Signed-off-by: Martin Schwidefsky <schwidefsky@de.ibm.com>

arch/s390/kernel/smp.c

@@ -788,14 +788,14 @@ static ssize_t show_idle_time(struct sys_device *dev, char *buf)
 	}
 	new_time = idle->idle_time;
 	spin_unlock_irq(&idle->lock);
-	return sprintf(buf, "%llu us\n", new_time >> 12);
+	return sprintf(buf, "%llu\n", new_time >> 12);
 }
-static SYSDEV_ATTR(idle_time, 0444, show_idle_time, NULL);
+static SYSDEV_ATTR(idle_time_us, 0444, show_idle_time, NULL);
 
 static struct attribute *cpu_attrs[] = {
 	&attr_capability.attr,
 	&attr_idle_count.attr,
-	&attr_idle_time.attr,
+	&attr_idle_time_us.attr,
 	NULL,
 };