powerpc/mpc85xx_ds: convert to unified PCI init

Similar to how the primary PCI bridge is identified by looking
for an isa subnode, we determine whether to apply uli exclusions
by looking for a uli subnode.

Signed-off-by: Scott Wood <scottwood@freescale.com>
Signed-off-by: Kumar Gala <galak@kernel.crashing.org>