freedreno: immediates upload cleanups and new asserts
In !5810 (merged) it was suggested that I put my constant data in the shader BO, and in cleaning up to do that we should probably put immediates there too, like the closed driver does.
I took a stab at it, but the alignment requirements for indirect uploads look maybe more onerous than we want to introduce for immediates. In the absence of performance data, I'm not ready to push that. However, I like the cleanups I made along the way and I think the new asserts are a good idea to keep for the next person that stumbles into indirect const uploads land.