[virglrenderer-devel] first pass at ssbo support

[Dave Airlie]

Hey,

This is a first pass at extracting the SSBO code from the gles3.1 work.

Mesa branch is
https://gitlab.freedesktop.org/airlied/mesa/tree/virgl-ssbo-submit

It's slightly changed vs the gl-4.3 branch and is not compatible at all.

I'm not quite finished I don't think, but I think I should have enough
to make sure I don't at least cause any piglit regressions.

Dave.