Fix issue 4604090: notification sound interrupted.

The problem is that the audio HAL fails to acquire the wake lock when playing the notification.
This is because of a change that removed the mediaserver process form the system group for honeycomb.

The fix consists in requesting the wake lock from PowerManagerService when AudioFlinger mixer
wakes up.

A consequence of this change is that audio HALs or pcm drivers do not have to hold wake locks
anymore as in the past.

Change-Id: I4fb3cc84816c9c408ab7fec75886baf801e1ecb5
diff --git a/services/audioflinger/Android.mk b/services/audioflinger/Android.mk
index a0407b9..fa49592 100644
--- a/services/audioflinger/Android.mk
+++ b/services/audioflinger/Android.mk
@@ -21,7 +21,8 @@
     libhardware \
     libhardware_legacy \
     libeffects \
-    libdl
+    libdl \
+    libpowermanager
 
 LOCAL_STATIC_LIBRARIES := \
     libcpustats \