Enable MIGRAPHX_MLIR_TUNING_CFG generation when defined

[richagadgil]

MIGRAPHX_ENABLE_MLIR=1 MIGRAPHX_MLIR_TUNING_CFG=../unet.cfg /code/AMDMIGraphX/build/bin/migra
phx-driver compile /models/resnet50_v1.onnx

[codecov[bot]]

Codecov Report

All modified and coverable lines are covered by tests :white_check_mark:

Project coverage is 92.18%. Comparing base (2f97579) to head (f6e01f0). Report is 12 commits behind head on develop.

Additional details and impacted files

```diff @@ Coverage Diff @@ ## develop #3616 +/- ## ======================================== Coverage 92.18% 92.18% ======================================== Files 513 513 Lines 21548 21578 +30 ======================================== + Hits 19863 19891 +28 - Misses 1685 1687 +2 ```

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