nv50/ir/opt: CALLs cannot load
nv50/ir/ssa: add a few comments regarding RenamePass
MERGE mark SULDP call as builtin
MERGE don't do stuff on builtin indrect calls
MERGE nve4_compute.c random change
nv50/ir: print function inputs and outputs
nv50/ir/ra: make sure all used function inputs get assigned a reg

A live range [0, 0) counts as empty. For function inputs this can
be a problem, so insert a nop at the beginning to make it [0, 1).
This is a bit of a hack but also the most simple solution.