Add the audio decoder variant of QMediaPlayer.

Rather than the probe based way of doing it.  Initially private.

Change-Id: I30005f8da22f6451cb9de8eb3f0e193838d48c93
Reviewed-by: Ling Hu <ling.hu@nokia.com>
Reviewed-by: Jonas Rabbe <jonas.rabbe@nokia.com>

src/multimedia/qmediaserviceproviderplugin.h

@@ -218,6 +218,14 @@ public:
 */
 #define Q_MEDIASERVICE_RADIO "com.nokia.qt.radio"
 
+/*!
+    Service with support for decoding audio.
+    Required Controls: QAudioDecoderControl
+    Optional: that streams control
+*/
+#define Q_MEDIASERVICE_AUDIODECODER "com.nokia.qt.audiodecode"
+
+
 
 QT_END_NAMESPACE