powerpc/mpc85xx: Add workaround for erratum A-005125

In a very rare condition, a system hang is possible when the e500 core
initiates a guarded load to PCI / PCIe /SRIO performs a coherent write
to memory. Please refer to errata document for more details. This erratum
applies to the following SoCs and their variants, if any.

BSC9132
BSC9131
MPC8536
MPC8544
MPC8548
MPC8569
MPC8572
P1010
P1020
P1021
P1022
P1023
P2020
C29x

Signed-off-by: York Sun <yorksun@freescale.com>
CC: Scott Wood <scottwood@freescale.com>