[llvm] [SystemZ] Use scheduling model for load latency (PR #217617)

[Jonas Paulsson via llvm-commits]

JonPsson1 wrote:

With a proper benchmarking run over night, I got mixed results with the SelectOptimize pass. Overall it was very close to a zero difference.

```
main <> SelectOptimize enabled

Improvements:
0.979: i500.perlbench_r
0.989: f511.povray_r
...
Regressions:
1.024: i523.xalancbmk_r
...
```

https://github.com/llvm/llvm-project/pull/217617