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/video/qabstractvideosurface.cpp

@@ -50,6 +50,17 @@
 
 QT_BEGIN_NAMESPACE
 
+namespace
+{
+    class QAbstractVideoSurfacePrivateRegisterMetaTypes
+    {
+    public:
+        QAbstractVideoSurfacePrivateRegisterMetaTypes()
+        {
+            qRegisterMetaType<QAbstractVideoSurface::Error>();
+        }
+    } _registerMetaTypes;
+}
 
 
 class QAbstractVideoSurfacePrivate {