[S390] Don't use small stacks when lockdep is used.

The lock dependency validator adds a bunch of extra stack frames to
the stack, which can cause stack overflows. Especially seen on 31 bit
where the small stack is only 4k.

Signed-off-by: Heiko Carstens <heiko.carstens@de.ibm.com>
Signed-off-by: Martin Schwidefsky <schwidefsky@de.ibm.com>

arch/s390/Kconfig

@@ -178,7 +178,7 @@ config PACK_STACK
 
 config SMALL_STACK
 	bool "Use 4kb/8kb for kernel stack instead of 8kb/16kb"
-	depends on PACK_STACK
+	depends on PACK_STACK && !LOCKDEP
 	help
 	  If you say Y here and the compiler supports the -mkernel-backchain
 	  option the kernel will use a smaller kernel stack size. For 31 bit