amd64_edac: Cleanup chipselect handling

Add a struct representing the DRAM chip select base/limit register
pairs. Concentrate all CS handling in a single function. Also, add CS
looping macros for cleaner, more readable code. While at it, adjust code
to F15h. Finally, do smaller macro names cleanups (remove family names
from register macros) and debug messages clarification.

No functional change.

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