[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/vmlinux.scr

@@ -0,0 +1,10 @@
+SECTIONS
+{
+  .rodata.compressed : {
+	input_len = .;
+	LONG(input_data_end - input_data) input_data = .;
+	*(.data)
+	output_len = . - 4;
+	input_data_end = .;
+	}
+}