Arm backend: ArmTester support testing with portable ops

[zingo]

Summary

This will enable model testing where some ops are not fully delegated,
like done in the backend flow test suite.

This also remove the unused fast_fvp pytest flag and always run the
Corstone-300/320 in fast mode as we are never interesting in PMU cycle
numbers in the pytesting anyway, this gives more then a 2x speedboost
on some models.

This will also extend the FVP timeout to 20 min for backend flows and
increase allocation pool to 80MB to make it possible to tests larger
models.

For normal unit tests the timeout is set to 10 min

Test plan

Arm backend suite test will tests this.

cc @freddan80 @per @oscarandersson8218 @digantdesai

[pytorch-bot]

🔗 Helpful Links

🧪 See artifacts and rendered test results at hud.pytorch.org/pr/pytorch/executorch/15278

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❗ 1 Active SEVs

There are 1 currently active SEVs. If your PR is affected, please view them below:

• Long queue for ROCM runners, also B200 and XPU queueing is observed

❌ 2 New Failures, 1 Cancelled Job, 2 Unrelated Failures

As of commit 61c6310 with merge base 94ce147 ():

NEW FAILURES - The following jobs have failed:

• pull / android / run-emulator (gh)
  The process '/usr/bin/sh' failed with exit code 255
• pull / unittest-editable / macos / macos-job (gh)
  examples/models/test/test_export.py::ExportTest::test_mv3_export_to_executorch

CANCELLED JOB - The following job was cancelled. Please retry:

• trunk / test-models-macos-cpu (mobilebert, xnnpack-quantization-delegation) / macos-job (gh)
  ##[error]The operation was canceled.

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

• trunk / unittest-release / macos / macos-job (gh) (similar failure)
  [ FAILED ] WavLoaderTest.LoadAudioDataRejectsUnsupportedFormat

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

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

• trunk / unittest-release / linux / linux-job (gh) (trunk failure)
  [ FAILED ] WavLoaderTest.LoadAudioDataRejectsUnsupportedFormat

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[zingo]

Failed tests are unrelated