ntt: Collapse move constant offsets into the CONST[0][A0.x+offset] field.

The r300 DX9 wine failure I looked at was due to addressing math immediates taking up space in the uniform file, which if we could bake it into the CONST file offset we wouldn't need at all. nv30 and softpipe would like this, too.

My thought is to add a base field to load_ubo_vec4, and then use nir_opt_offsets to pull the constants out. Going to take a bit of auditing of current users to see how they feel, though.