float8 matmul bench: make peak tops lookup dynamic

[vkuzo]

Summary:

Instead of hardcoding H100 numbers, makes the script choose between H100
and B200 based on available GPU.

Test Plan:

python benchmarks/float8/bench_matmul.py

Reviewers:

Subscribers:

Tasks:

Tags:

[vkuzo]

Stack from ghstack (oldest at bottom):

• enable compile with mxfp8 and mxfp4 cutlass gemm #1838
• add mxfp8_cublas recipe to mx_formats #1831
• float8 matmul benchmark: hook up cublas mxfp8 gemm #1830
• -> float8 matmul bench: make peak tops lookup dynamic #1829

[pytorch-bot]

🔗 Helpful Links

🧪 See artifacts and rendered test results at hud.pytorch.org/pr/pytorch/ao/1829

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As of commit 535a51a with merge base d8af7d7 ():
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