[S390] Randomize lower bits of stack address

Randomize the lower bits of the stack address like x86 and powerpc.

Signed-off-by: Heiko Carstens <heiko.carstens@de.ibm.com>
Signed-off-by: Martin Schwidefsky <schwidefsky@de.ibm.com>
diff --git a/arch/s390/include/asm/system.h b/arch/s390/include/asm/system.h
index 6710b0e..8f8d759 100644
--- a/arch/s390/include/asm/system.h
+++ b/arch/s390/include/asm/system.h
@@ -449,7 +449,7 @@
 extern void (*_machine_halt)(void);
 extern void (*_machine_power_off)(void);
 
-#define arch_align_stack(x) (x)
+extern unsigned long arch_align_stack(unsigned long sp);
 
 static inline int tprot(unsigned long addr)
 {