s390/cmpxchg: select HAVE_CMPXCHG_LOCAL option

Now that hopefully all cmpxchg/xchg bugs have been fixed select
HAVE_CMPXCHG_LOCAL option which uncovered a couple of bugs on s390.

The only call site which is affected seems to be within mm/vmstat.c.
Signed-off-by: Heiko Carstens <heiko.carstens@de.ibm.com>
Signed-off-by: Martin Schwidefsky <schwidefsky@de.ibm.com>

arch/s390/Kconfig

@@ -93,6 +93,7 @@ config S390
 	select ARCH_SAVE_PAGE_KEYS if HIBERNATION
 	select HAVE_MEMBLOCK
 	select HAVE_MEMBLOCK_NODE_MAP
+	select HAVE_CMPXCHG_LOCAL
 	select ARCH_DISCARD_MEMBLOCK
 	select ARCH_INLINE_SPIN_TRYLOCK
 	select ARCH_INLINE_SPIN_TRYLOCK_BH