s390/cpuinfo: show maximum thread id

Expose the maximum thread id with /proc/cpuinfo.
With the new line the output looks like this:

vendor_id       : IBM/S390
bogomips per cpu: 20325.00
max thread id   : 1

With this new interface it is possible to always tell the correct
number of cpu threads potentially being used by the kernel.
Signed-off-by: Heiko Carstens <heiko.carstens@de.ibm.com>
Signed-off-by: Martin Schwidefsky <schwidefsky@de.ibm.com>

arch/s390/kernel/processor.c

@@ -104,6 +104,7 @@ static void show_cpu_summary(struct seq_file *m, void *v)
 		   "bogomips per cpu: %lu.%02lu\n",
 		   num_online_cpus(), loops_per_jiffy/(500000/HZ),
 		   (loops_per_jiffy/(5000/HZ))%100);
+	seq_printf(m, "max thread id   : %d\n", smp_cpu_mtid);
 	seq_puts(m, "features\t: ");
 	for (i = 0; i < ARRAY_SIZE(hwcap_str); i++)
 		if (hwcap_str[i] && (elf_hwcap & (1UL << i)))