target-s390: add firmware code

This patch adds a firmware blob to the S390 target. The blob is a simple
implementation of a virtio client that tries to read the second stage
bootloader from sectors described as of offset 0x20 in the MBR.

In combination with an updated zipl this allows for booting from virtio
block devices. This firmware is built from the same sources as the second
stage bootloader. You can find a virtio capable s390-tools in this repo:

git://repo.or.cz/s390-tools.git

Signed-off-by: Alexander Graf <agraf@suse.de>
Signed-off-by: Aurelien Jarno <aurelien@aurel32.net>
diff --git a/Makefile b/Makefile
index eb9e02b..306a1a4 100644
--- a/Makefile
+++ b/Makefile
@@ -184,7 +184,8 @@
 pxe-ne2k_pci.bin pxe-pcnet.bin \
 pxe-rtl8139.bin pxe-virtio.bin \
 bamboo.dtb petalogix-s3adsp1800.dtb \
-multiboot.bin linuxboot.bin
+multiboot.bin linuxboot.bin \
+s390-zipl.rom
 else
 BLOBS=
 endif