x86/PCI: Export pci_walk_bus function.

In preperation of modularizing Xen-pcifront the pci_walk_bus
needs to be exported so that the xen-pcifront module can walk
call the pci subsystem to walk the PCI devices and claim them.

Signed-off-by: Jeremy Fitzhardinge <jeremy.fitzhardinge@citrix.com>
Signed-off-by: Konrad Rzeszutek Wilk <konrad.wilk@oracle.com>
Acked-by: Jesse Barnes <jbarnes@virtuousgeek.org> [http://marc.info/?l=linux-pci&m=126149958010298&w=2]
diff --git a/drivers/pci/bus.c b/drivers/pci/bus.c
index 7f0af0e..69546e9 100644
--- a/drivers/pci/bus.c
+++ b/drivers/pci/bus.c
@@ -299,6 +299,7 @@
 	}
 	up_read(&pci_bus_sem);
 }
+EXPORT_SYMBOL_GPL(pci_walk_bus);
 
 EXPORT_SYMBOL(pci_bus_alloc_resource);
 EXPORT_SYMBOL_GPL(pci_bus_add_device);