Fix XNNPACK Prelu for non-4d tensors

[GregoryComer]

Summary: Prelu with non-4d tensors is broken on xnnpack. This is because the channels last reshape pass assumes that it must be 4d. Update the pass to leave non-4d tensors unmodified. We still treat all 4d tensors as NHWC, though theoretically you could have a 4d tensor + prelu in a non-CV model, but I'm inclined to just leave this for now. We can add smarter 4d handling later if needed.

Differential Revision: D98987039

[pytorch-bot]

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⚠️ 1 Awaiting Approval, 2 Unrelated Failures

As of commit 87849e1 with merge base 186eb4b ():

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

• periodic (gh)

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 / windows / windows-job (gh) (trunk failure)
  ##[error]The operation was canceled.
• pull / unittest-editable / windows / windows-job (gh) (trunk failure)
  ##[error]The operation was canceled.

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@GregoryComer has exported this pull request. If you are a Meta employee, you can view the originating Diff in D98987039.

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