[S390] add support for compressed kernels

Add the "bzImage" compile target and the necessary code  to generate
compressed kernel images. The old style uncompressed "image" target
is preserved, a simple make will build them both.

Signed-off-by: Martin Schwidefsky <schwidefsky@de.ibm.com>
diff --git a/arch/s390/kernel/Makefile b/arch/s390/kernel/Makefile
index 20f8612..64230bc 100644
--- a/arch/s390/kernel/Makefile
+++ b/arch/s390/kernel/Makefile
@@ -29,6 +29,7 @@
 obj-y	+= $(if $(CONFIG_64BIT),reipl64.o,reipl.o)
 
 extra-y				+= head.o init_task.o vmlinux.lds
+extra-y				+= $(if $(CONFIG_64BIT),head64.o,head31.o)
 
 obj-$(CONFIG_MODULES)		+= s390_ksyms.o module.o
 obj-$(CONFIG_SMP)		+= smp.o topology.o