soc: qcom: spcom: maintain wakeup window when active packet exchange

This change activate PM wakeup source in following way:
1. Activate on receive a spcom request from SPU
2. Close window in the end of packet exchange or timeout:
   - end of tx of spcom response to SPU (server case)
   - end of delivery of spcom request to usersace (client case)
   - timeout for handling a packet exchange for 2 seconds

Change-Id: Ibbb6ba9870226299e5731fda6133c3dde780ca25
Signed-off-by: Konstantin Dorfman <kdorfman@codeaurora.org>