x86/devicetree: Use generic PCI <-> OF matching

Instead of walking the whole PCI tree to update the of_node's for
PCI busses and devices after the fact, enable the new generic core
code for doing so by providing the proper device nodes for the
PCI host bridges

Signed-off-by: Benjamin Herrenschmidt <benh@kernel.crashing.org>
Acked-by: Grant Likely <grant.likely@secretlab.ca>
Tested-by: Sebastian Andrzej Siewior <bigeasy@linutronix.de>