NIR NOLTIS (instruction selection), v3d use of it

@idr has been working on rewriting backend codegen in i965 based on nir_search, and I happened to be working on the other half of the instruction selection problem: given a bunch of possible instructions to generate for groups ("tiles") of NIR instructions, which ones should we pick?

Right now the v3d backend conversion is not pretty, but I think with idr's work we can end up with something very nice for less-orthogonal architectures (v3d doesn't have a lot of opportunities for selection, but vc4 certainly does).