CoreAudio: Create an audio plugin supporting iOS and OS X

This removes the Mac audio backend that was hardcoded into QtMultimedia
and adds a new audio plugin using the CoreAudio API.

Change-Id: Ib15291825f9452a3763e0eeb281d952deb0bad3d
Reviewed-by: Richard Moe Gustavsen <richard.gustavsen@digia.com>
Reviewed-by: Christian Stromme <christian.stromme@digia.com>
Reviewed-by: Yoann Lopes <yoann.lopes@digia.com>

tests/auto/integration/qaudiooutput/tst_qaudiooutput.cpp

@@ -829,8 +829,9 @@ void tst_QAudioOutput::pushSuspendResume()
 
     audioOutput.resume();
 
-    // Give backends running in separate threads a chance to resume.
-    QTest::qWait(100);
+    // Give backends running in separate threads a chance to resume
+    // but not too much or the rest of the file may be processed
+    QTest::qWait(20);
 
     // Check that QAudioOutput immediately transitions to ActiveState
     QVERIFY2((stateSignal.count() == 1),