AVFoundation: Enable use of QMediaPlayer for audio on iOS

This commit disables the video components of the AVFoundation
mediaplayer backend when building for iOS and enables the use of
QMediaPlayer with audio assets.

Change-Id: Iadd6f9c61ed1e656301326e90a22cbca6428b654
Reviewed-by: Richard Moe Gustavsen <richard.gustavsen@digia.com>
AVFoundation: Use CoreAnimation to render video to QVideoWidget

Previously a QGLWidget was used as a target for the
AVFVideoFrameRenderer.  This was uncessary as it is possible to render
directly on top of the QWidget using the CoreAnimation Framework.

Change-Id: I08923c85fd56c8874c1d8c187ae5145e220fab92
Reviewed-by: Richard Moe Gustavsen <richard.gustavsen@digia.com>
AVFoundation: Enable QVideoWidget on iOS

Change-Id: I88041e7a2ea052fe449542eeaada31c09d93d163
Reviewed-by: Richard Moe Gustavsen <richard.gustavsen@digia.com>
AVFoundation: Basic camera support for iOS

Enables basic software rendering support for iOS.

Change-Id: Icd29076ea627295819ede6d9680de576ba39b34e
Reviewed-by: Richard Moe Gustavsen <richard.gustavsen@digia.com>