powerpc/pci: Export pci_add_device_node_info()

This renames update_dn_pci_info() to pci_add_device_node_info()
with corresponding adjustment on the parameter type and exports it.
The function is used to create pdn (struct pci_dn) for the indicated
device node. Another function add_pdn(), almost wrapper of
pci_add_device_node_info(), to be used in traverse_pci_devices(). No
logical changes introduced.

Signed-off-by: Gavin Shan <gwshan@linux.vnet.ibm.com>
Reviewed-by: Alexey Kardashevskiy <aik@ozlabs.ru>
Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>