[Cherry-pick][RESOLVED] [BACKEND] Restrict MMAV5/MMV3 usage for N < 16 and fix no-swizzle case (#7981) (#538)

Summary:
⚠️ **MERGE CONFLICTS DETECTED** ⚠️

This cherry-pick contains merge conflicts that require manual resolution.

Original Commit: d91d182
Original Author: Thomas Raoux
Original Date: 2025-08-26 22:22:01 -0700

**Action Required:**
1. Check out this branch locally
2. Resolve the merge conflicts in the affected files
3. Commit the resolved changes
4. Update this PR

Original commit message:
```
[BACKEND] Restrict MMAV5/MMV3 usage for N < 16 and fix no-swizzle case (#7981)

This prevent generating miscompiles for cases where the N dimension is
too small. Technically we could support N=8 but it would require padding
the shared memory.
```

This PR was automatically cherry-picked from the upstream triton-lang/triton repository.
The conflicts have been committed with conflict markers for easier resolution.

Pull Request resolved: #538

Reviewed By: dshi7

Differential Revision: D85907170

Pulled By: agron911

fbshipit-source-id: 7633f7c08d1774d0fac4f51027685cbfb18b1be8

Author: agron911