powerpc/mpc85xx: software workaround for DDR erratum A-004468

Boot space translation utilizes the pre-translation address to select
the DDR controller target. However, the post-translation address will be
presented to the selected DDR controller. It is possible that the pre-
translation address selects one DDR controller but the post-translation
address exists in a different DDR controller when using certain DDR
controller interleaving modes. The device may fail to boot under these
circumstances. Note that a DDR MSE error will not be detected since DDR
controller bounds registers are programmed to be the same when configured
for DDR controller interleaving.

Signed-off-by: York Sun <yorksun@freescale.com>
Signed-off-by: Andy Fleming <afleming@freescale.com>