[PATCH/RESEND 0/2] sched: re-add removed arch_update_cpu_topology call

[Heiko Carstens <heiko.carstens@de.ibm.com>]

This fixes a regression introduced with
e761b7725234276a802322549cee5255305a0930 ("cpu hotplug, sched:
Introduce cpu_active_map and redo sched domain managment (take 2)":

arch_reinit_sched_domains used to call arch_update_cpu_topology
via arch_init_sched_domains. This call got lost with the above
mentioned patch.

So we might end up with outdated and missing cpus in the cpu core
maps (s390 used to call arch_reinit_sched_domains if cpu topology changed).

This patch set changes arch_update_cpu_topology so that it can indicate
if the cpu topology changed and adds a call to arch_update_cpu_topology
in partition_sched_domains which gets called whenever scheduling domains
get updated.
So whenever architecture code detects that cpu topology changed it might
force an update of the scheduling domains by calling arch_reinit_sched_domains
or rebuild_sched_domains.

Besides that the first patch also adds a comment to arch_update_cpu_topology
so that its purpose gets described, since most people seem to expect that
cpu core mappings are stable which isn't necessarily the case.