s390: switch to generic kernel_thread()

Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>
diff --git a/arch/s390/Kconfig b/arch/s390/Kconfig
index 107610e..5744239 100644
--- a/arch/s390/Kconfig
+++ b/arch/s390/Kconfig
@@ -125,6 +125,7 @@
 	select GENERIC_CLOCKEVENTS
 	select KTIME_SCALAR if 32BIT
 	select HAVE_ARCH_SECCOMP_FILTER
+	select GENERIC_KERNEL_THREAD
 
 config SCHED_OMIT_FRAME_POINTER
 	def_bool y