qom: introduce root device

This is based on Jan's suggestion for how to do unique naming.  The root device
is the root of composition.  All devices are reachable via child<> links from
this device.

Signed-off-by: Anthony Liguori <aliguori@us.ibm.com>

hw/container.c

@@ -0,0 +1,20 @@
+#include "sysbus.h"
+
+static int container_initfn(SysBusDevice *dev)
+{
+    return 0;
+}
+
+static SysBusDeviceInfo container_info = {
+    .init = container_initfn,
+    .qdev.name = "container",
+    .qdev.size = sizeof(SysBusDevice),
+    .qdev.no_user = 1,
+};
+
+static void container_init(void)
+{
+    sysbus_register_withprop(&container_info);
+}
+
+device_init(container_init);