Amend platform intrinsics documentation

[adpaco-aws]

Description of changes:

Updates support value for intrinsics in #1942. Makes clear where the SIMD operations come from.

Testing:

• How is this change tested? Docs change.

• Is this a refactor change? No.

Checklist

• Each commit message has a non-empty body, explaining why the change was made
• Methods or procedures are documented
• Regression or unit tests are included, or existing tests cover the modified code
• My PR is restricted to a single feature or bugfix

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