The host_buses list is an odd structure - a list of pointers to PCI root
buses existing in parallel to the normal qdev tree structure.  This patch
removes it, instead putting the link pointers into the PCIHostState
structure, which have a 1:1 relationship to PCIHostBus structures anyway.
Signed-off-by: NDavid Gibson <david@gibson.dropbear.id.au>
Signed-off-by: NMichael S. Tsirkin <mst@redhat.com>