tst_ncpus_conf: Instead of the old tst_ncpus_max

In commit 84d608326c59b7177c8ad4228fbcd21569b4f2fd we have updated tst_ncpus_max
function. But smt_smp_enabled.sh and smt_smp_affinity.sh need the old
tst_ncpus_max, otherwise they will fail. Use tst_ncpus_conf instead of the old
tst_ncpus_max function.

Signed-off-by: Zeng Linggang <zenglg.jy@cn.fujitsu.com>
Acked-by: Jan Stancek <jstancek@redhat.com>
Signed-off-by: Wanlong Gao <gaowanlong@cn.fujitsu.com>