Qualcomm AI Engine Direct - Docs Update

[winskuo-quic]

Summary

Community user has reported that some QNN docs are outdated. #21880
This PR updates the doc.

Test plan

NA

[pytorch-bot]

🔗 Helpful Links

🧪 See artifacts and rendered test results at hud.pytorch.org/pr/pytorch/executorch/21971

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✅ No Failures

As of commit 1069abb with merge base bea0657 ():
💚 Looks good so far! There are no failures yet. 💚

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[github-actions]

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