sched: walt: Derive sched_smp_overlap_capacity from the energy-model

The energy-model indicates the OPP at which spreading the tasks across
cluster is beneficial for power. This OPP would be the overlapping
point of the power curves of the lower and higher clusters. Derive
the sched_smp_overlap_capacity to the capacity corresponding to such
overlapping point. No such overlapping point exists on a big.LITTLE
system.

Change-Id: I75686597042726a6c91c4403903d919a67bce880
Signed-off-by: Pavankumar Kondeti <pkondeti@codeaurora.org>