radeonsi: allow out-of-order rasterization in commutative blending cases

radeonsi: allow out-of-order rasterization in commutative blending cases

We do not enable this by default for additive blending, since it slightly
breaks OpenGL invariance guarantees due to non-determinism.

Still, there may be some applications can benefit from white-listing
via the radeonsi_commutative_blend_add drirc setting without any real
visible artifacts.

Reviewed-by: Marek Olšák <marek.olsak@amd.com>
Tested-by: Dieter Nützel <Dieter@nuetzel-hh.de>