This patch pulls the PCI-related junk out of struct device_node and
puts it in a separate structure, struct pci_dn.  The device_node now
just has a void * pointer in it, which points to a struct pci_dn for
nodes that represent PCI devices.  It could potentially be used in
future for device-specific data for other sorts of devices, such as
virtual I/O devices.

Signed-off-by: Paul Mackerras <paulus@samba.org>