NXP backend: Add NXP backend tutorial page

[pytorchbot]

Summary

Adds tutorial page for NXP backend.

Test plan

Documentation built locally using Makefile without any problems.

cc @robert-kalmar @JakeStevens @digantdesai

[pytorch-bot]

🔗 Helpful Links

🧪 See artifacts and rendered test results at hud.pytorch.org/pr/pytorch/executorch/14853

• 📄 Preview Python docs built from this PR

Note: Links to docs will display an error until the docs builds have been completed.

❌ 5 New Failures, 2 Cancelled Jobs

As of commit 90afa0d with merge base e0dda90 ():

NEW FAILURES - The following jobs have failed:

• pull / test-models-linux-basic (mv3, portable, cmake, linux.arm64.2xlarge, executorch-ubuntu-22.04-gcc11... / linux-job (gh)
  RuntimeError: Command docker exec -t 90ab786e80700bae6c7e33e69280382b09a88dd734fd24e4ee610d13e99882fd /exec failed with exit code 1
• pull / test-vulkan-models-linux / linux-job (gh)
  RuntimeError: Command docker exec -t 0238acc5d256ce143119c6288ca48a65f240f9b0afb18dcaaacaf71768f2bfff /exec failed with exit code 56
• pull / test-vulkan-operators-linux / linux-job (gh)
  RuntimeError: Command docker exec -t 38655fc48c01244221eab82b7c46534f806a847bd9674745f63ed8d80a06bb52 /exec failed with exit code 56
• pull / unittest / linux / linux-job (gh)
  RuntimeError: Command docker exec -t 38a63e7015d2cfb9afaf18a9d7965a9e7eae5b3564e3db743a23ffbccb44a8e0 /exec failed with exit code 56
• pull / unittest-editable / linux / linux-job (gh)
  RuntimeError: Command docker exec -t 11ad6a3fd89c05fc33206ac090cf9cc3b4f82768f14d3e466a64172dcecdd660 /exec failed with exit code 56

CANCELLED JOBS - The following jobs were cancelled. Please retry:

• pull / unittest / macos / macos-job (gh)
  ##[error]The operation was canceled.
• pull / unittest-editable / macos / macos-job (gh)
  ##[error]The operation was canceled.

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[GregoryComer]

As this is a doc-only change, I'm not re-running the flaky CI jobs.