amd64_edac: add driver header

Borislav:
- remove register bit descriptions (complete text in BKDG)
- cleanup and remove excessive/superfluous comments

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>