virgl: Gravity mark doesn't render properly in OpenGL mode with ARB_buffer_storage support

Running the Tellusim Gravity mark benchmark in OpenGL mode on VirGL doesn't draw the actual scene when ARB_buffer_storage is enabled. The benchmark starts, but when it is actually supposed to render the scene it just sits there. Eventually it will print a frame rate and score on the screen, but these numbers don't make much sense. Same goes for the GLES version of the benchmark. It may happen that the output that counts up the initialization time flickers between two frames.

A trace taken with apitrace actually replays fine on the host hardware, so this is most likely a bug in virgl or virglrenderer.