Add HIP conversion file outputs to .gitignore (#5111)

This PR adds the following HIP output files to `.gitignore`:
``` 
*_hip.cpp
*_hip.h
*.hip
*.cuh
*hip_layers.h
```

---------

Co-authored-by: Michael Wyatt <michaelwyatt@microsoft.com>

.gitignore

@@ -53,3 +53,10 @@ docs/code-docs/build
 ## Testing data
 # Saved checkpoints for testing
 tests/unit/saved_checkpoint/
+
+# HIP files created during AMD compilation
+*_hip.cpp
+*_hip.h
+*.hip
+*.cuh
+*hip_layers.h