drm/msm/sde: separate the power notify and idle notify events

Commit e17e0ee2 ("drm/msm/sde: clean up idle pc
notification implementation") merges the power on/off
and idle timeout notification. However, this is not required.
Client is interested in idle timeout notification based on
last frame update instead of when certain display is entering
or existing in power collapse state. This change separates
both notifications to avoid mismatch at client side.

Change-Id: Ic933ec490cdc89a2e1b024072d8b4a197fd8daed
Signed-off-by: Dhaval Patel <pdhaval@codeaurora.org>
Signed-off-by: Jayant Shekhar <jshekhar@codeaurora.org>