amd64_edac: add EDAC core-related initializers

Borislav:

- add a amd64_free_mc_sibling_devices() helper instead of opencoding the
  release-path.
- fix/cleanup comments
- fix function return value patterns
- cleanup debug 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>