Adds a pass to lower specified
load_attribute_deltas plus ALU instructions.
The configurability is because in some common cases I can do this with a single
bary.f instruction instead.
The first patch is kinda unrelated other than it is prep work for freedreno/ir3 support for various
interpolateAtXYZ(). (I'll also end up needing additional lowering for
load_barycentric_at_sample but that involves some new instructions that I still need to figure out exactly what they are doing)