[S390] lockless idle time accounting

Replace the spinlock used in the idle time accounting with a sequence
counter mechanism analog to seqlock.

Signed-off-by: Martin Schwidefsky <schwidefsky@de.ibm.com>
diff --git a/arch/s390/include/asm/cputime.h b/arch/s390/include/asm/cputime.h
index ec917d4..7a3817a 100644
--- a/arch/s390/include/asm/cputime.h
+++ b/arch/s390/include/asm/cputime.h
@@ -178,7 +178,7 @@
 }
 
 struct s390_idle_data {
-	spinlock_t lock;
+	unsigned int sequence;
 	unsigned long long idle_count;
 	unsigned long long idle_enter;
 	unsigned long long idle_time;