edac:i82975x fix 32bit compile and cleanup

the clean up achieves:
  1. fix warning on 32-bit compile
  2. reorder info extraction for clarity
  3. add error-trap diagnostic message
  4. handle ALL modes of memory configurations

Signed-off-by: Arvind R. <arvino55@gmail.com>
Signed-off-by: Jiri Kosina <jkosina@suse.cz>