QAudioOutput: low-latency related changes.

- Decrease timer period to 10ms;
- Set PulseAudio buffer size if specified by the user;
- Set PulseAudio buffer size to 40ms if not specified;
- Always request 1 chunk of data at a time in pull mode;

Change-Id: If95c097c67c3342f733bde9e699518741d7ef991
Reviewed-by: Dmytro Poplavskiy <dmytro.poplavskiy@nokia.com>

src/plugins/pulseaudio/qaudiooutput_pulse.h

@@ -122,10 +122,12 @@ private:
     bool m_opened;
     QIODevice *m_audioSource;
     QTimer m_periodTimer;
+    int m_periodTime;
     pa_stream *m_stream;
     int m_notifyInterval;
     int m_periodSize;
     int m_bufferSize;
+    int m_maxBufferSize;
     QTime m_clockStamp;
     qint64 m_totalTimeValue;
     QTimer *m_tickTimer;