[S390] register cpu devices for SMP=n

A kernel compiled with SMP=n will not register any cpu devices.
The resulting kernel image will not boot with this error message:

    kernel BUG at fs/sysfs/group.c:65!

Use GENERIC_CPU_DEVICES=y if SMP=n to get the missing cpu device.
Signed-off-by: Martin Schwidefsky <schwidefsky@de.ibm.com>

arch/s390/Kconfig

@@ -64,6 +64,7 @@ config ARCH_SUPPORTS_DEBUG_PAGEALLOC
 config S390
 	def_bool y
 	select USE_GENERIC_SMP_HELPERS if SMP
+	select GENERIC_CPU_DEVICES if !SMP
 	select HAVE_SYSCALL_WRAPPERS
 	select HAVE_FUNCTION_TRACER
 	select HAVE_FUNCTION_TRACE_MCOUNT_TEST