NIR loop unrolling is already enabled so just let it do its job.
Shader-db results (nv120):
total gpr in shared programs: 893490 -> 893898 (0.05%)
gpr in affected programs: 15338 -> 15746 (2.66%)
total instructions in shared programs: 6243205 -> 6237068 (-0.10%)
instructions in affected programs: 71160 -> 65023 (-8.62%)
total bytes in shared programs: 66729616 -> 66664760 (-0.10%)
bytes in affected programs: 759328 -> 694472 (-8.54%)
Reviewed-by: Emma Anholt <emma@anholt.net>
Part-of: <https://gitlab.freedesktop.org/mesa/mesa/-/merge_requests/16366>
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