fix build with QT_NO_GRAPHICSVIEW

QGraphicsItem is not available if QT_NO_GRAPHICSVIEW is defined,
but this was not checked when building QGraphicsSvgItem.

Change-Id: I24b9f784d12a9ce4cbf5a4ffd22690c6441f6118
Reviewed-by: Friedemann Kleint <Friedemann.Kleint@theqtcompany.com>
Reviewed-by: aavit <eirik.aavitsland@theqtcompany.com>