sched: simplify the group load balancer

While thinking about the previous patch - I realized that using per domain
aggregate load values in load_balance_fair() is wrong. We should use the
load value for that CPU.

By not needing per domain hierarchical load values we don't need to store
per domain aggregate shares, which greatly simplifies all the math.

It basically falls apart in two separate computations:
 - per domain update of the shares
 - per CPU update of the hierarchical load

Also get rid of the move_group_shares() stuff - just re-compute the shares
again after a successful load balance.

Signed-off-by: Peter Zijlstra <a.p.zijlstra@chello.nl>
Cc: Srivatsa Vaddagiri <vatsa@linux.vnet.ibm.com>
Cc: Mike Galbraith <efault@gmx.de>
Signed-off-by: Ingo Molnar <mingo@elte.hu>