Do not expose to scheduler caches of single CPU.

Before this change my dual-Xeon(R) Gold 6242R always reported 3 levels
or topology (root, package/L3 and core/L2). But with SMT disabled
core/L2 matches thread, so additional topology level only causes more
traversal work. With this change SMT case is reported same as before,
while non-SMT is reported with only 2 much more simple levels.

MFC after: 2 weeks