amd64_edac: add helper to dump relevant registers

Borislav:

- cleanup/fix comments
- fix function return value patterns
- cleanup dbg calls

Reviewed-by: Mauro Carvalho Chehab <mchehab@redhat.com>
Signed-off-by: Doug Thompson <dougthompson@xmission.com>
Signed-off-by: Borislav Petkov <borislav.petkov@amd.com>