Fixing the broken unit tests caused by missing portable lib import.

[jirioc]

Summary

Adding missing portable lib import.

Test plan

This is a fix for broken NXP unit tests.

cc @digantdesai @JakeStevens @robert-kalmar

[pytorch-bot]

🔗 Helpful Links

🧪 See artifacts and rendered test results at hud.pytorch.org/pr/pytorch/executorch/14014

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As of commit 19ea5c0 with merge base 3899beb ():
💚 Looks good so far! There are no failures yet. 💚

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[pytorch-bot]

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[digantdesai]

Thank you! Why we didn't see this in the CI?