Rename QtMultimediaKit to QtMultimedia.

There are a few legacy bits left in place so it passes CI, and
then qt5.git etc can be updated.

Change-Id: I6b082e50e6958c72fdabc2974992e16d90dafa3a
Reviewed-on: http://codereview.qt-project.org/5368
Reviewed-by: Qt Sanity Bot <qt_sanity_bot@ovi.com>
Reviewed-by: Jonas Rabbe <jonas.rabbe@nokia.com>

src/plugins/v4l/radio/v4lradiocontrol.h

@@ -65,7 +65,7 @@ public:
     ~V4LRadioControl();
 
     bool isAvailable() const;
-    QtMultimediaKit::AvailabilityError availabilityError() const;
+    QtMultimedia::AvailabilityError availabilityError() const;
 
     QRadioTuner::State state() const;