xen: Add initialisation of Xen

The xenpv machine use the common init function.

Signed-off-by: Anthony PERARD <anthony.perard@citrix.com>
Acked-by: Alexander Graf <agraf@suse.de>
Signed-off-by: Alexander Graf <agraf@suse.de>

xen-stub.c

@@ -0,0 +1,15 @@
+/*
+ * Copyright (C) 2010       Citrix Ltd.
+ *
+ * This work is licensed under the terms of the GNU GPL, version 2.  See
+ * the COPYING file in the top-level directory.
+ *
+ */
+
+#include "qemu-common.h"
+#include "hw/xen.h"
+
+int xen_init(void)
+{
+    return -ENOSYS;
+}