lscpu: use maximum CPU speed from DMI, avoid duplicate version string

lscpu: use maximum CPU speed from DMI, avoid duplicate version string

* Read maximum CPU speed from DMI
* Don't use max speed if nonsensical
* Avoid appending "CPU @ speed" to the version string if it's already included.
  (This is a code robustness improvement as DMI is currently read for ARMs only,
   and the issue was detected on Intel.)

Fixes: https://github.com/util-linux/util-linux/commit/a772d7c493afcec32f0123fc947013f74db6e45d
Signed-off-by: Karel Zak <kzak@redhat.com>