PCI: factor pci_bus_add_child() from pci_bus_add_devices()

This patch splits a new function, pci_bus_add_child(), from
pci_bus_add_devices(). The new function can be used to register PCI
buses to the device core.

Signed-off-by: Yu Zhao <yu.zhao@intel.com>
Signed-off-by: Jesse Barnes <jbarnes@virtuousgeek.org>

drivers/pci/pci.h

diff --git a/drivers/pci/pci.h b/drivers/pci/pci.h
index c4f4a1e..d1e92d8 100644
--- a/drivers/pci/pci.h
+++ b/drivers/pci/pci.h
@@ -173,6 +173,7 @@
 				struct resource *res, unsigned int reg);
 extern int pci_resource_bar(struct pci_dev *dev, int resno,
 			    enum pci_bar_type *type);
+extern int pci_bus_add_child(struct pci_bus *bus);
 extern void pci_enable_ari(struct pci_dev *dev);
 /**
  * pci_ari_enabled - query ARI forwarding status