Implement QAudioDeviceInfo operator==/!=

Compares some of the useful parts, but perhaps should be made more
tolerant.

Also refactored the auto test to properly skip if there are no
(output) devices, rather than manually skip.

Task-number: QTBUG-13723
Change-Id: I3b83f87a440a83f4237fa119a23009bc99e7626a
Reviewed-by: Jonas Rabbe <jonas.rabbe@nokia.com>
Reviewed-by: Dmytro Poplavskiy <dmytro.poplavskiy@nokia.com>

src/multimedia/audio/qaudiodeviceinfo.h

@@ -76,6 +76,9 @@ public:
 
     QAudioDeviceInfo& operator=(const QAudioDeviceInfo& other);
 
+    bool operator==(const QAudioDeviceInfo &other) const;
+    bool operator!=(const QAudioDeviceInfo &other) const;
+
     bool isNull() const;
 
     QString deviceName() const;