x86, cacheinfo: Calculate L3 indices

We need to know the valid L3 indices interval when disabling them over
/sysfs. Do that when the core is brought online and add boundary checks
to the sysfs .store attribute.

Signed-off-by: Borislav Petkov <borislav.petkov@amd.com>
LKML-Reference: <1264172467-25155-6-git-send-email-bp@amd64.org>
Signed-off-by: H. Peter Anvin <hpa@zytor.com>