power_policy: Lock stream list fix race condition

Add mutex locks in audio power_policy routines & stream close
routines to fix race condition causing use after free situation
leading to audio service crash

Change-Id: I6b7427daf8c5c281327c92b281c89040368012cf
Signed-off-by: Aravind Siddappaji <quic_asiddapp@quicinc.com>