s390/smp: improve setup of possible cpu mask

Since under z/VM we cannot have more than 64 cpus, make sure the
cpu_possible_mask does not contain more bits.
This avoids wasting memory for dynamic per-cpu allocations if
CONFIG_NR_CPUS is larger than 64.

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

arch/s390/kernel/setup.c

@@ -1023,6 +1023,7 @@ void __init setup_arch(char **cmdline_p)
 	setup_vmcoreinfo();
 	setup_lowcore();
 
+	smp_fill_possible_mask();
         cpu_init();
 	s390_init_cpu_topology();