sb_edac: correctly fetch DIMM width on Ivy Bridge and Haswell

dimm_dev_type has been incorrectly determined in sb_edac. This patch fixes it
for Ivy Bridge and Haswell only since nothing like exists for Sandy Bridge.
We tested this patch in multiple systems matching the results with the
installed memory modules.

Acked-by: Tony Luck <tony.luck@intel.com>
Signed-off-by: Aristeu Rozanski <aris@redhat.com>
Signed-off-by: Mauro Carvalho Chehab <mchehab@osg.samsung.com>