sched: Separate out build of ALLNODES sched groups from __build_sched_domains

For the sake of completeness.
Now all calls to init_sched_build_groups() are contained in
build_sched_groups().

Signed-off-by: Andreas Herrmann <andreas.herrmann3@amd.com>
Cc: Peter Zijlstra <peterz@infradead.org>
LKML-Reference: <20090818110013.GK29515@alberich.amd.com>
Signed-off-by: Ingo Molnar <mingo@elte.hu>