NXP backend: Remove dependency on the non-edge operator aten.max_pool2d.default.

[MartinPavella]

Summary

The max_pool2d_with_indices is an edge operator that produces 2 outputs, so getitem nodes must follow it. That's why in the early stages of our ExecuTorch endeavor, Lukas found an XNNPACK pass to replace these ops with just a single max_pool2d. As this is an aten dialect only operator, we had to force ExecuTorch to ignore it and there were other connected issues.

A recent PR bent the use of this aten dialect operator even further, so I decided to clean it all up and provide a robust support for the max_pool2d_with_indices, without introducing any non-edge dialect operators.

Test plan

Unit-tests provided.

cc @robert-kalmar @JakeStevens @digantdesai

[pytorch-bot]

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❌ 1 Awaiting Approval, 3 New Failures, 1 Pending, 2 Unrelated Failures

As of commit 7f031e2 with merge base 389ea94 ():

AWAITING APPROVAL - The following workflow needs approval before CI can run:

• periodic (gh)

NEW FAILURES - The following jobs have failed:

• pull / test-samsung-models-linux / linux-job (gh)
  RuntimeError: Command docker exec -t af152c3c4f93570079e4cce84f1330af9f17b7168252ca9209aba3bf5e951417 /exec failed with exit code 1
• pull / test-samsung-quantmodels-linux / linux-job (gh)
  RuntimeError: Command docker exec -t 840a6f86b171ca166b503c9e48f4093edf396f6468d9dc366164a3c653b69fc6 /exec failed with exit code 1
• pull / unittest-nxp-neutron / linux-job (gh)
  RuntimeError: Command docker exec -t dd6a58485da6cc2fd130239f8de7f2b5638b6e5fd53c07f5631ed5316cbeed4b /exec failed with exit code 1

BROKEN TRUNK - The following jobs failed but were present on the merge base:

👉 Rebase onto the `viable/strict` branch to avoid these failures

• pull / unittest / macos / macos-job (gh) (trunk failure)
  AttributeError: '_OpNamespace' 'mkldnn' object has no attribute '_is_mkldnn_acl_supported'
• pull / unittest-editable / macos / macos-job (gh) (trunk failure)
  AttributeError: '_OpNamespace' 'mkldnn' object has no attribute '_is_mkldnn_acl_supported'

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