edac: new ppc4xx driver module

This adds support for an EDAC memory controller adaptation driver for the
"ibm,sdram-4xx-ddr2" ECC controller realized in the AMCC PowerPC 405EX[r].

At present, this driver has been developed and tested against the
controller realization in the AMCC PPC405EX[r] on the AMCC Kilauea and
Haleakala boards (256 MiB w/o ECC memory soldered onto the board) and a
proprietary board based on those designs (128 MiB ECC memory, also
soldered onto the board).

In the future, dynamic feature detection and handling needs to be added
for the other realizations of this controller found in the 440SP, 440SPe,
460EX, 460GT and 460SX.

Eventually, this driver will likely be evolved and adapted to the above
variant realizations of this controller as well as broken apart to handle
the other known ECC-capable controllers prevalent in other PPC4xx
processors:

  - IBM SDRAM (405GP, 405CR and 405EP) "ibm,sdram-4xx"
  - IBM DDR1 (440GP, 440GX, 440EP and 440GR) "ibm,sdram-4xx-ddr"
  - Denali DDR1/DDR2 (440EPX and 440GRX) "denali,sdram-4xx-ddr2"

[akpm@linux-foundation.org: coding-style fixes]
Signed-off-by: Grant Erickson <gerickson@nuovations.com>
Signed-off-by: Doug Thompson <dougthompson@xmission.com>
Cc: Benjamin Herrenschmidt <benh@kernel.crashing.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>