NXP backend: Improve cifarnet speed by removing the initial pading.

[jirioc]

Summary

NXP backend: Improve cifarnet speed by removing the initial pading.

Test plan

Update to test_remove_io_quant_ops_pass__cifarnet() is part of the diff.

[pytorch-bot]

🔗 Helpful Links

🧪 See artifacts and rendered test results at hud.pytorch.org/pr/pytorch/executorch/13279

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✅ You can merge normally! (3 Unrelated Failures)

As of commit 18cdd96 with merge base 72580d2 ():

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

• trunk / unittest-release / macos / macos-job (gh) (similar failure)
  backends/xnnpack/test/ops/test_conv1d.py::TestConv1d::test_qs8_conv1d_batchnorm_seq

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

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

• Apple / build-demo-ios / macos-job (gh) (trunk failure)
  RuntimeError: Command bash /Users/runner/work/_temp/exec_script failed with exit code 65
• pull / unittest / macos / macos-job (gh) (trunk failure)
  backends/xnnpack/test/ops/test_conv1d.py::TestConv1d::test_qs8_conv1d_batchnorm_seq

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