[POWERPC] pci32: Use generic pci_assign_unassign_resources

This makes the 32 bits PowerPC PCI code use the generic code to assign
resources to devices that had unassigned or conflicting resources.

This allow us to remove the local implementation that was incomplete and
could not assign for example a PCI<->PCI bridge from scratch, which is
needed on various embedded platforms.

Signed-off-by: Benjamin Herrenschmidt <benh@kernel.crashing.org>
Signed-off-by: Paul Mackerras <paulus@samba.org>