lscpu: print correct number of threads per core if possible

lscpu: print correct number of threads per core if possible

lscpu calculates the number of threads per core by dividing the number
of online cpus with the number of cores. This may or may not give the
correct number of threads per core depending on the number of online
CPUs (and which CPUs are online).

At least on s390 there is a new "max thread id" field within
/proc/cpuinfo present which reliably allows us to tell the number of
threads per core. Let's use this instead, like we already have also
special treatment to figure out the number core per socket etc. on
s390.

Signed-off-by: Heiko Carstens <heiko.carstens@de.ibm.com>