Arm backend: extend Softmax to handle dim < 0

[oscarandersson8218]

Change-Id: I8c88964ac70efc59466bfc48dfc11f784f3beffa

[pytorch-bot]

🔗 Helpful Links

🧪 See artifacts and rendered test results at hud.pytorch.org/pr/pytorch/executorch/4819

• 📄 Preview Python docs built from this PR

Note: Links to docs will display an error until the docs builds have been completed.

❌ 1 New Failure, 1 Unrelated Failure

As of commit 9a04c37 with merge base d8a00e6 ():

NEW FAILURE - The following job has failed:

• trunk / test-llama-runner-mac (fp32, buck2, xnnpack+kv+custom) / macos-job (gh)
  RuntimeError: Command bash /Users/ec2-user/runner/_work/_temp/exec_script failed with exit code 1

FLAKY - The following job failed but was likely due to flakiness present on trunk:

• trunk / test-models-macos (cmake, mul, portable, macos-m1-stable, 90) / macos-job (gh) (detected as infra flaky with no log or failing log classifier)

This comment was automatically generated by Dr. CI and updates every 15 minutes.

[facebook-github-bot]

@digantdesai has imported this pull request. If you are a Meta employee, you can view this diff on Phabricator.