[WiP] gallium: Work in progress on OpenFIMG driver

Changes:
 - emit attribute setup and vertex context only if relevant state was
   dirty (can save up to 50% overhead with very small batches aka
   es2gears),
 - move structure fields around a bit to optimize cache usage,
 - don't re-emit program state on vertex/texture changes,
 - don't mark FBs/textures busy using the old way, as this will be
   tracked by cpu_prep/fini() calls.