x86, cacheinfo: Add cache index disable sysfs attrs only to L3 caches

The cache_disable_[01] attribute in

/sys/devices/system/cpu/cpu?/cache/index[0-3]/

is enabled on all cache levels although only L3 supports it. Add it only
to the cache level that actually supports it.

Signed-off-by: Borislav Petkov <borislav.petkov@amd.com>
LKML-Reference: <1264172467-25155-5-git-send-email-bp@amd64.org>
Signed-off-by: H. Peter Anvin <hpa@zytor.com>