nv30/40: Switch to using NIR-to-TGSI by default.

nv30/40: Switch to using NIR-to-TGSI by default.

shader-db results (note that we expect many more loops unrolled, so instr
count is probably understating the win):

nv30:
total instructions in shared programs: 16535069 -> 14299105 (-13.52%)
instructions in affected programs: 16377286 -> 14141322 (-13.65%)
total gpr in shared programs: 81255 -> 67268 (-17.21%)
gpr in affected programs: 56714 -> 42727 (-24.66%)
LOST:   0
GAINED: 824

nv40:
total instructions in shared programs: 20907673 -> 18428749 (-11.86%)
instructions in affected programs: 20755510 -> 18276586 (-11.94%)
total gpr in shared programs: 104200 -> 82831 (-20.51%)
gpr in affected programs: 80278 -> 58909 (-26.62%)

14130

Part-of: <https://gitlab.freedesktop.org/mesa/mesa/-/merge_requests/14130>