pm: policy: change the policy event handling

Some events needs to be handled with a very low latency constraint.
If the system is in deep sleep, exit latency from this low level state
exceeds sometimes the maximum latency constraint of these events.

Before suspending the system, select which events is happening sooner,
kernel events or normal events.
CPU will be up just before the next event occurs taking into account the
exit latency of the current power state

Change also the policy event API to take as argument absolute time in HW
cycles instead of time in us

Signed-off-by: Riadh Ghaddab <rghaddab@baylibre.com>