x86, cacheinfo: Fix disabling of L3 cache indices

* Correct the masks used for writing the cache index disable indices.
* Do not turn off L3 scrubber - it is not necessary.
* Make sure wbinvd is executed on the same node where the L3 is.
* Check for out-of-bounds values written to the registers.
* Make show_cache_disable hex values unambiguous
* Check for Erratum #388

Signed-off-by: Borislav Petkov <borislav.petkov@amd.com>
LKML-Reference: <1264172467-25155-4-git-send-email-bp@amd64.org>
Signed-off-by: H. Peter Anvin <hpa@zytor.com>