NXP backend: Building MCUXpresso example

[jirioc]

Summary

This commit enables to build and run the ExecuTorch CIFARNet application for the NXP RT700 platform using the MCUXpresso SDK and the GNU Arm Embedded Toolchain.

Test plan

The application was built and it produces valid classification result.

cc @robert-kalmar@JakeStevens@digantdesai@rascani

[pytorch-bot]

🔗 Helpful Links

🧪 See artifacts and rendered test results at hud.pytorch.org/pr/pytorch/executorch/21140

• 📄 Preview Python docs built from this PR

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❌ 2 New Failures

As of commit b4d811f with merge base 80a07e6 ():

NEW FAILURES - The following jobs have failed:

• pull / test-samsung-models-linux / linux-job (gh)
  AttributeError: type object 'Test_Milestone_MobileBertFinetune' has no attribute 'model_cache_dir'
• trunk / test-multimodal-macos (gemma3-4b) / macos-job (gh)
  executorch

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[linux-foundation-easycla]

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[jirioc]

It was decided that the west system will be used to build the SDK. With this, the whole build process can be tested using CI.

[roman-janik-nxp]

Successfully tested test_build_from_scratch.sh script 👍 .

[roman-janik-nxp]

@jirioc@robert-kalmar Have you thought about extending this example for other backends relevant for RT700, e.g Cortex-M and Cadence? Maybe the placement of these files could be outside nxp dir. The part after AoT would be the same / similar for those backends.