Add qRegisterMetaTypes for the public Q_DECLARE_METATYPEs.

Also turned qtmedianamespace.qdoc into a cpp file so I
could stick the qRegisterMetaTypes into it.

Change-Id: Idd6d3e2f348f1ed45b0a35ce180d023a170e8625
Reviewed-by: Jonas Rabbe <jonas.rabbe@nokia.com>

src/multimedia/qcameraimageprocessingcontrol.cpp

@@ -44,6 +44,18 @@
 
 QT_BEGIN_NAMESPACE
 
+namespace
+{
+    class QCameraImageProcessingControlPrivateRegisterMetaTypes
+    {
+    public:
+        QCameraImageProcessingControlPrivateRegisterMetaTypes()
+        {
+            qRegisterMetaType<QCameraImageProcessingControl::ProcessingParameter>();
+        }
+    } _registerMetaTypes;
+}
+
 /*!
     \class QCameraImageProcessingControl
     \inmodule QtMultimedia