panfrost: Lower transform feedback to compute
Panfrost has an implementation of transform feedback by laying out varyings according to the requested transform feedback layout. This works because varyings on Bifrost and older are purely software allocated. On Valhall, varyings are hardware allocated so this no longer works. Instead, we need to lower away the transform feedback. This MR adds a compute shader based lowering that passes the ES3.1 CTS on Valhall.
Edited by Alyssa Rosenzweig