common_audio: Re-enable WebRtcSpl_AddSatW32() and WebRtcSpl_SubSatW32() optimizations on armv7

According to the issue, common_audio_unittests failed on armv7. It currently pass, so we should turn it on again. There is no print out in the issue, so the cause of failure is unknown.

BUG=740
TESTED=locally on N7
R=tina.legrand@webrtc.org

Review URL: https://webrtc-codereview.appspot.com/14199004

git-svn-id: http://webrtc.googlecode.com/svn/trunk@6975 4adac7df-926f-26a2-2b94-8c16560cd09d