Setting the flag QSurfaceFormat::StereoBuffers does not actually do
anything, because we do not utilize the extra buffers provided. We need
to expose setting the correct buffers using glDrawBuffers between draw
calls.
Change-Id: I6a5110405e621030ac3a2886fa83df0cfe928723
Reviewed-by: Laszlo Agocs <laszlo.agocs@qt.io>
