Improve AMD GCN detection fallback

[rasbid]

Summary

• allow AMD GCN detection to rely on shader core wavefront size when integer dot product or subgroup size control extensions are missing
• record when VK_EXT_subgroup_size_control is unavailable so later feature requests can avoid it while still treating the GPU as GCN
• log the detected device architecture at startup to confirm GCN-specific paths engage on hardware such as the RX 580

Testing

• not run (not requested)

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https://chatgpt.com/codex/tasks/task_e_68ebe20eb94c8330b838cab5c032b354