ntt: Switch to new-style registers and modifiers
Use all the nir_legacy.h features to transition away from the deprecated
structures. shader-db is quite happy. I assume that's a mix of more aggressive
source mod usage and better coalescing (nir-to-tgsi doesn't copyprop).
total instructions in shared programs: 900179 -> 886881 (-1.48%)
instructions in affected programs: 562077 -> 548779 (-2.37%)
helped: 5198
HURT: 470
Instructions are helped.
total temps in shared programs: 91165 -> 91530 (0.40%)
temps in affected programs: 13906 -> 14271 (2.62%)
helped: 651
HURT: 847
Temps are HURT.
Cc @anholt