amd64_edac: add ECC reporting initializers

Borislav:
- convert to the new {rd|wr}msr_on_cpus interfaces.
- convert pvt->old_mcgctl to a bitmask thus saving some bytes
- fix/cleanup comments
- fix function return value patterns
- add a proper bugfix found by Doug to amd64_check_ecc_enabled where we
  missed checking for the ECC enabled bit in NB CFG.
- 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>