[Tools:Feature] llm_bench: add '-fa' meaning whether to use flash att…

[v0jiuqi]

…ention(default 1, using flash attention)

Discussed-in: Merge-Request 28749507 , URL: https://code.alibaba-inc.com/AliNN/AliNNPrivate/codereview/28749507
GitOrigin-RevId: 6f6b024d4e4c3f23a483aed5e7d0443102295a6f

Description

Module

Type

• Feature
• Bugfix
• Perf
• Refact
• Style
• Doc
• Test
• Chore

Checklist

• Commit message follows [Module:Type] Description format
• Code compiles without errors
• Tested on relevant platform(s)
• No unrelated format or style changes included

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