[ROCm][CI] Fix test_cudagraph_mode.py Failure For AMD CI

[micah-wil]

After #26847 was merged, we are seeing failures in AMD CI in the v1/cudagraph/test_cudagraph_mode.py test with errors like DID NOT RAISE <class 'Exception'>.

=========================== short test summary info ============================
FAILED v1/cudagraph/test_cudagraph_mode.py::test_cudagraph_compilation_combo[RocmAttn-PIECEWISE-0-False]
FAILED v1/cudagraph/test_cudagraph_mode.py::test_cudagraph_compilation_combo[RocmAttn-FULL_AND_PIECEWISE-0-False]
============= 2 failed, 12 passed, 3 warnings in 289.02s (0:04:49) =============

The problem was just that the supported field was updated for the CUDA backend test but not the ROCm backend in the combo_cases_2 test case. Further, this happened because of a change I made last week in #29367 which introduced some code duplication that I have fixed here so that we can avoid these types of errors in the future.

With this PR, I am again seeing the following when running pytest -v -s v1/cudagraph/test_cudagraph_mode.py:

================================================================ warnings summary ================================================================
<frozen importlib._bootstrap>:488
  <frozen importlib._bootstrap>:488: DeprecationWarning: builtin type SwigPyPacked has no __module__ attribute

<frozen importlib._bootstrap>:488
  <frozen importlib._bootstrap>:488: DeprecationWarning: builtin type SwigPyObject has no __module__ attribute

-- Docs: https://docs.pytest.org/en/stable/how-to/capture-warnings.html
=================================================== 14 passed, 2 warnings in 211.22s (0:03:31) ===================================================

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[gemini-code-assist]

Code Review

This pull request addresses a CI failure on ROCm for test_cudagraph_mode.py by correcting the supported flag in test cases. The main improvement is the refactoring that removes duplicated code for ROCm and CUDA test configurations, replacing it with a unified setup. This not only fixes the immediate issue but also enhances maintainability and reduces the likelihood of similar bugs in the future. The change is clean, correct, and a good improvement to the test suite.