sched: Make the scheduler aware of C-state for cpus

C-state represents a power-state of a cpu. A cpu could have one or
more C-states associated with it. C-state transitions are based on
various factors (expected sleep time for example). "Deeper" C-states
implies longer wakeup latencies.

Scheduler needs to know wakeup latency associated with various C-states.
Having this information allows the scheduler to make better decisions
during task placement. For example:

- Prefer an idle cpu that is in the least shallow C-state
- Avoid waking up small tasks on a idle cpu unless it is in the least
  shallow C-state

This patch introduces APIs in the scheduler that can be used by the
architecture specific power-management driver to inform the scheduler
about C-states for cpus.

Change-Id: I39c5ae6dbace4f8bd96e88f75cd2d72620436dd1
Signed-off-by: Srivatsa Vaddagiri <vatsa@codeaurora.org>
Signed-off-by: Syed Rameez Mustafa <rameezmustafa@codeaurora.org>