power: apply wait callback mechanism to all state transitions

power: apply wait callback mechanism to all state transitions

Generalize sleep-wait mechanism. It now always waits on changing state
if some other processes has registered change-state-wait on the state.
On transition to a next state, remove all change-state-waits that
waiting for other than the next state. If a timeout expires or all
change-state-waits are confirmed, invoke wait-done callback.

Change-Id: I573ca68c3a6c210cad479e068ee088d6a31ba54f
Signed-off-by: Youngjae Cho <y0.cho@samsung.com>