[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>

arch/s390/boot/compressed/head64.S

@@ -0,0 +1,48 @@
+/*
+ * Startup glue code to uncompress the kernel
+ *
+ * Copyright IBM Corp. 2010
+ *
+ *   Author(s):	Martin Schwidefsky <schwidefsky@de.ibm.com>
+ */
+
+#include <linux/init.h>
+#include <asm/asm-offsets.h>
+#include <asm/thread_info.h>
+#include <asm/page.h>
+#include "sizes.h"
+
+__HEAD
+	.globl	startup_continue
+startup_continue:
+	basr	%r13,0			# get base
+.LPG1:
+	# setup stack
+	lg	%r15,.Lstack-.LPG1(%r13)
+	aghi	%r15,-160
+	brasl	%r14,decompress_kernel
+	# setup registers for memory mover & branch to target
+	lgr	%r4,%r2
+	lg	%r2,.Loffset-.LPG1(%r13)
+	la	%r4,0(%r2,%r4)
+	lg	%r3,.Lmvsize-.LPG1(%r13)
+	lgr	%r5,%r3
+	# move the memory mover someplace safe
+	la	%r1,0x200
+	mvc	0(mover_end-mover,%r1),mover-.LPG1(%r13)
+	# decompress image is started at 0x11000
+	lgr	%r6,%r2
+	br	%r1
+mover:
+	mvcle	%r2,%r4,0
+	jo	mover
+	br	%r6
+mover_end:
+
+	.align	8
+.Lstack:
+	.quad	0x8000 + (1<<(PAGE_SHIFT+THREAD_ORDER))
+.Loffset:
+	.quad	0x11000
+.Lmvsize:
+	.quad	SZ__bss_start