s390/boot: make head.S and als.c be part of the decompressor only

Since uncompressed kernel image does not have to be bootable anymore,
move head.S, head_kdump.S and als.c to boot/ folder and compile them
in just in the decompressor.

Reviewed-by: Heiko Carstens <heiko.carstens@de.ibm.com>
Signed-off-by: Vasily Gorbik <gor@linux.ibm.com>
Signed-off-by: Martin Schwidefsky <schwidefsky@de.ibm.com>
diff --git a/arch/s390/Makefile b/arch/s390/Makefile
index ea3e610..d25fbc1 100644
--- a/arch/s390/Makefile
+++ b/arch/s390/Makefile
@@ -113,8 +113,7 @@
 
 OBJCOPYFLAGS	:= -O binary
 
-head-y		:= arch/s390/kernel/head.o
-head-y		+= arch/s390/kernel/head64.o
+head-y		:= arch/s390/kernel/head64.o
 
 # See arch/s390/Kbuild for content of core part of the kernel
 core-y		+= arch/s390/