nv50/ir: restructure and rename postraconstantfolding pass

we might want to add more folding passes here, so make it a bit more generic

v2: leave the comment and reword commit message
v4: rename it to PostRaLoadPropagation

Signed-off-by: Karol Herbst <karolherbst@gmail.com>
Reviewed-by: Samuel Pitoiset <samuel.pitoiset@gmail.com>
Reviewed-by: Ilia Mirkin <imirkin@alum.mit.edu>
1 file changed