feat: keep eplb for pure prefill and optimize remap and record

[JiaoliangYu]

Motivation

• Keep rebalance only during the prefill phase, step and loading count only for prefill
• fused triton kernel for remap and record, 150+us -> ~20us

Technical Details

Test Plan

Test Result

Submission Checklist

• Look over the contributing guidelines at https://github.com/ROCm/ROCm/blob/develop/CONTRIBUTING.md#pull-requests.

[github-actions]

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