PCI: add busn_res in struct pci_bus

This adds a busn_res resource in struct pci_bus.  This will replace the
secondary/subordinate members and will be used to build a bus number
resource tree to help with bus number allocation.

[bhelgaas: changelog]
CC: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Yinghai Lu <yinghai@kernel.org>
Signed-off-by: Bjorn Helgaas <bhelgaas@google.com>

include/linux/pci.h

@@ -419,6 +419,7 @@ struct pci_bus {
 	struct list_head slots;		/* list of slots on this bus */
 	struct resource *resource[PCI_BRIDGE_RESOURCE_NUM];
 	struct list_head resources;	/* address space routed to this bus */
+	struct resource busn_res;	/* bus numbers routed to this bus */
 
 	struct pci_ops	*ops;		/* configuration access functions */
 	void		*sysdata;	/* hook for sys-specific extension */