ppc/8xxx: Delete PCI nodes from device tree if not configured

If the PCI controller wasn't configured or enabled delete from the
device tree (include its alias).

For the case that we didn't even configure u-boot with knowledge of
the controller we can use the fact that the pci_controller pointer
is NULL to delete the node in the device tree.  We determine that
a controller was not setup (because of HW config) based on the fact
that cfg_addr wasn't setup.

Signed-off-by: Kumar Gala <galak@kernel.crashing.org>