[ROCm] Enable TestCUDABackward::test_backward unit tests (#3849)
* Workaround to pass unit/ops/accelerators/test_accelerator_backward.py unit tests on ROCm
* Rearranged is_rocm_pytorch()
* Introduced is_rocm_pytorch() for ROCm
* Fixed formatting errors
* Function call
* formatting fix
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Co-authored-by: Logan Adams <114770087+loadams@users.noreply.github.com>
Co-authored-by: Logan Adams <loadams@microsoft.com>