Cortex-M backend: Add cmsis_nn pybind dependency

[Erik-Lundell]

- Add cmsis_nn to new optional-dependency called [cortex_m]

- Additionally, add an install step that allows optional
depedencies to install required build tools. This is needed
for cortex_m.

- Add cmsis_nn to backends/cortex_m/requirements-cortex-m.txt
and add possibility to install from setup.sh to not break
backwards compatability, and to mirror ethos_u and vgf backend.

- Add guard to cortex_m/passes/__init__.py to fail gracefully if
cortex_m dependencies are not installed.

cc @digantdesai @freddan80 @per @zingo @oscarandersson8218 @mansnils @Sebastian-Larsson @robell

[pytorch-bot]

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❌ 1 New Failure, 1 Cancelled Job, 3 Unrelated Failures

As of commit 646ccb7 with merge base 524f037 ():

NEW FAILURE - The following job has failed:

• pull / unittest-editable / linux / linux-job (gh)
  examples/models/test/test_export.py::ExportTest::test_ic3_export_to_executorch

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

• periodic / gather-models (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 / macos / macos-job (gh) (trunk failure)
  ##[error]The operation was canceled.
• pull / unittest-editable / macos / macos-job (gh) (trunk failure)
  ##[error]The operation was canceled.
• trunk / unittest-release / macos / macos-job (gh) (trunk failure)
  ##[error]The operation was canceled.

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