Moved QMediaServiceProvider to private header.

It's not intended to be used by applications.

Change-Id: I2acc26180ebb5c2419438169827f39aaf4578389
Reviewed-by: Michael Goddard <michael.goddard@nokia.com>

src/multimedia/multimedia.pro

@@ -26,6 +26,7 @@ PRIVATE_HEADERS += \
     qmediaobject_p.h \
     qmediapluginloader_p.h \
     qmediaservice_p.h \
+    qmediaserviceprovider_p.h \
 
 PUBLIC_HEADERS += \
     qmediabindableinterface.h \
@@ -33,7 +34,6 @@ PUBLIC_HEADERS += \
     qmediaenumdebug.h \
     qmediaobject.h \
     qmediaservice.h \
-    qmediaserviceprovider.h \
     qmediaserviceproviderplugin.h \
     qmediatimerange.h \
     qtmedianamespace.h \