memory: Move owner-less MemoryRegions to /machine/unattached

This cleans up the official /machine namespace. In particular
/machine/system[0] and /machine/io[0], as well as entries with
non-sanitized node names such as "/machine/qemu extended regs[0]".

The actual MemoryRegion names remain unchanged.
Acked-by: NPaolo Bonzini <pbonzini@redhat.com>
Tested-by: NAlistair Francis <alistair.francis@xilinx.com>
Signed-off-by: NAndreas Färber <afaerber@suse.de>

memory.c

@@ -868,7 +868,7 @@ void memory_region_init(MemoryRegion *mr,
                         uint64_t size)
 {
     if (!owner) {
-        owner = qdev_get_machine();
+        owner = container_get(qdev_get_machine(), "/unattached");
     }
 
     object_initialize(mr, sizeof(*mr), TYPE_MEMORY_REGION);