radv: Use nir_opt_reuse_constants()

radv: Use nir_opt_reuse_constants()

Right now, this won't change much the shaders since most of the NIR constants
are reused in the NIR generated by SPIR-V, but will make radv resilient to
when that behavior change.

```
RADV GFX1100 results for radv fossils:

Totals:
Instrs: 71623585 -> 71623708 (+0.00%); split: -0.00%, +0.00%
CodeSize: 369326156 -> 369324312 (-0.00%); split: -0.00%, +0.00%
SpillSGPRs: 13576 -> 13586 (+0.07%)
Latency: 632889681 -> 632887831 (-0.00%); split: -0.00%, +0.00%
InvThroughput: 81674616 -> 81674859 (+0.00%); split: -0.00%, +0.00%
SClause: 2409601 -> 2409593 (-0.00%); split: -0.00%, +0.00%
Copies: 4063438 -> 4063579 (+0.00%); split: -0.00%, +0.01%
Branches: 1196703 -> 1196723 (+0.00%)
PreSGPRs: 4242897 -> 4243061 (+0.00%); split: -0.00%, +0.00%
PreVGPRs: 3926739 -> 3926742 (+0.00%)

Totals from 217 (0.16% of 133461) affected shaders:
Instrs: 353567 -> 353690 (+0.03%); split: -0.04%, +0.07%
CodeSize: 1790200 -> 1788356 (-0.10%); split: -0.15%, +0.04%
SpillSGPRs: 8 -> 18 (+125.00%)
Latency: 5152817 -> 5150967 (-0.04%); split: -0.05%, +0.01%
InvThroughput: 664273 -> 664516 (+0.04%); split: -0.03%, +0.06%
SClause: 10164 -> 10156 (-0.08%); split: -0.10%, +0.02%
Copies: 24225 -> 24366 (+0.58%); split: -0.32%, +0.90%
Branches: 7116 -> 7136 (+0.28%)
PreSGPRs: 13351 -> 13515 (+1.23%); split: -0.16%, +1.39%
PreVGPRs: 11583 -> 11586 (+0.03%)
```

Reviewed-by: Timur Kristóf <timur.kristof@gmail.com>
Part-of: <https://gitlab.freedesktop.org/mesa/mesa/-/merge_requests/5282>