audio: prevent larger than required sleeps - DO NOT MERGE

audio: prevent larger than required sleeps - DO NOT MERGE

This will be cherry picked into P build after O completes for other devices.

This reverts the revert from commit 2feb18ddfdbd20941ebcc3314780a582da5608e4.

b/17962037

From: Haynes Mathew George <hgeorge@codeaurora.org>
Date: Wed, 26 Mar 2014 16:18:42 -0700
Subject: [PATCH] AudioTrack: prevent larger than required sleeps

AudioTrackThread can end up waiting for larger than necessary
time for free space to be available in the cblk. Fix this by
waiting on the cblk futex instead of the (internal) condition variable.

Change-Id: Iba5b266f9b4082b3833f4abd52ebc6601c8e3034