intel/fs: Make the constant data part of the shader.
Instead of having the constant data be a bit that hangs off the NIR, it would be really convenient if the back-end compiler would just stuff it in the end of the program for us. We could add a couple new fields to
const_data_size. It wouldn't simplify state setup at all because we still have to set a UBO up for it but it would simplify shader caching quite a bit. Every extra bit of data with it's own size that's hanging off the side of the shader is a pain to cache.