xen: add blkback support

Signed-off-by: Ian Campbell <ian.campbell@citrix.com>
Signed-off-by: Jeremy Fitzhardinge <jeremy.fitzhardinge@citrix.com>
Signed-off-by: Konrad Rzeszutek Wilk <konrad.wilk@oracle.com>

Conflicts:

	drivers/xen/Makefile
diff --git a/drivers/xen/blkback/Makefile b/drivers/xen/blkback/Makefile
new file mode 100644
index 0000000..8bab63d
--- /dev/null
+++ b/drivers/xen/blkback/Makefile
@@ -0,0 +1,3 @@
+obj-$(CONFIG_XEN_BLKDEV_BACKEND) := blkbk.o
+
+blkbk-y	:= blkback.o xenbus.o interface.o vbd.o