btaa: subscribe to SystemSuspend for wakeup notification

This change initialize the SystemSuspend client at BTAA module and have
it subscribed to wakeup notification with wakeup reasons.

Tag: #feature
Bug: 170315554
Test: verified BTAA module receives wakeup notification
Change-Id: I6749a539f9a59f1893f4159cec6b7c9f517ead9d