amd64_edac: Remove DRAM base/limit subfields caching

Add a struct representing the DRAM base/limit range pairs and remove all
cached subfields. Replace them with accessor functions, which actually
saves us some space:

   text    data     bss     dec     hex filename
  14712    1577     336   16625    40f1 drivers/edac/amd64_edac_mod.o.after
  14831    1609     336   16776    4188 drivers/edac/amd64_edac_mod.o.before

Also, it simplifies the code a lot allowing to merge the K8 and F10h
routines.

No functional change.

Signed-off-by: Borislav Petkov <borislav.petkov@amd.com>