nir_to_tgsi: Enable nir_opt_move.

nir_to_tgsi: Enable nir_opt_move.

This moves some ops down to when they're needed, generally reducing the
number of temps in use.  It's not always a win -- sometimes you can end up
moving a generator of a component used by a nir_op_vec down, which means
that op's sources stay live while the vec (whose register likely gets
coalesced with the ops creating it) is also live.  But it's generally
good.

softpipe results:

temps in affected programs: 18115 -> 18026 (-0.49%)
imm in affected programs: 19 -> 22 (15.79%)

r300 results:

instructions in affected programs: 174 -> 178 (2.30%)
vinst in affected programs: 156 -> 160 (2.56%)
sinst in affected programs: 54 -> 50 (-7.41%)
temps in affected programs: 2634 -> 2169 (-17.65%)

Reviewed-by: Marek Olšák <marek.olsak@amd.com>
Part-of: <https://gitlab.freedesktop.org/mesa/mesa/-/merge_requests/14096>