Provide a way to cheaply flip your painted FBO

Provide a way to cheaply flip your painted FBO

After recent changes the painted images are upside down from previous
and there is no way to get at the texture coordinates to flip them back
without reimplementing QSGPainterNode and QSGPaintedItem.

This change adds only an enum and has minimal impact, while providing
useful functionality that also fixes this problem.

Change-Id: I6884da884d9303f6e08a984d4560cc7f7728d918
Reviewed-by: Sarah Jane Smith <sarah.j.smith@nokia.com>