PPC4xx: Make LWMON5 ECC POST board-independent

Hi Stefan (and group),

Here for your comments and suggestions are my proposed patches to take the ECC POST for the LWMON5 board and generalize it to all 440EPx/GRx boards. This code is running on our prototype Korat 440EPx boards.

I have replaced the volatile pointers with calls to in_be32() and out_be32(), but the synchronization between the writes creating the ECC errors and the reads to detect them is still required. I have left these changes in as I feel the code is clearer with them.

Please note that these patches require my previous patch to "include/ppc440.h".

Best regards,
Larry Johnson