AVFoundation: Fix y-inverted QML Videos

When the code that supports iOS was added, we introduced a bug where QML
videos would be played y-inverted on OS X.  This is because we made no
effort to y-invert the Framebuffer Object before rendering the texture
in the SceneGraph.  Now we render the video the the FBO y-inverted, so
there is no need to y-invert the resulting texture.

Task-number: QTBUG-35955
Change-Id: I41af1aaae57923b9972b5be5ec65f7d2a97d77c5
Reviewed-by: Yoann Lopes <yoann.lopes@digia.com>