powerpc: Fix boot hang regression on MPC8544DS

Commit 00c5372d

 caused the MPC8544DS
board to hang at boot.  The MPC8544DS is unique in that it doesn't use
the PCI slots on the ULI (unlike the MPC8572DS or MPC8610HPCD).  So
the dummy read at the end of the address space causes us to hang.

We can detect the situation by comparing the bridge's BARs versus
the root complex.

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