sched: add missing arch_update_cpu_topology() call

arch_reinit_sched_domains() used to call arch_update_cpu_topology()
via arch_init_sched_domains(). This call got lost with
e761b772

 ("cpu hotplug, sched: Introduce
cpu_active_map and redo sched domain managment (take 2)".

So we might end up with outdated and missing cpus in the cpu core
maps (architecture used to call arch_reinit_sched_domains if cpu
topology changed).

This adds a call to arch_update_cpu_topology in partition_sched_domains
which gets called whenever scheduling domains get updated. Which is
what is supposed to happen when cpu topology changes.

Signed-off-by: Heiko Carstens <heiko.carstens@de.ibm.com>
Signed-off-by: Ingo Molnar <mingo@elte.hu>