edac: add support for Calxeda highbank memory controller

Add support for memory controller on Calxeda Highbank platforms. Highbank
platforms support a single 4GB mini-DIMM with 1-bit correction and 2-bit
detection.

Signed-off-by: Rob Herring <rob.herring@calxeda.com>
Signed-off-by: Mauro Carvalho Chehab <mchehab@redhat.com>