EDAC/amd64: Merge sysfs debugging attributes setup code

There's no need for them to be in a separate file so merge them into the
main driver compilation unit like the other EDAC drivers do.

Drop now-unneeded function export, make the function static and shorten
static function names.

No functional changes.

Signed-off-by: Borislav Petkov <bp@suse.de>
Reviewed-by: Yazen Ghannam <yazen.ghannam@amd.com>
Link: https://lkml.kernel.org/r/20201215110517.5215-1-bp@alien8.de