[HIP] Optimized fused split GDR decode

[huizzhan]

Motivation

Added optimized hip kernel for fused split GDR decode.

Technical Details

Added optimized hip kernel (swizzled ssm_state) for fused split GDR decode implementation to support Qwen3Next.

Test Plan

Tested hip fused split GDR decode with different configs(itype/l2norm/input_shape/...).

Test Result

Evaluated perf with Qwen3Next (speedup x1.47 and x1.62 compared with origin triton implementation on TP4 and TP8 cases) and passed unit tests.

Submission Checklist

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

[github-actions]

🏷️ CI Guide

Runs automatically on every PR:

• ✅ Pre-checks (submodule verification, code formatting)
• ✅ Aiter op tests (gfx942 + gfx950)
• ✅ Triton tests (only when aiter/ops/triton/** or related paths are changed)

Extended tests (opt-in via labels):

Label	Tests
ci:sglang	SGLang integration tests
ci:atom	ATOM benchmark (DeepSeek-R1 + GPT-OSS)
ci:vllm	vLLM benchmark
ci:all	All of the above

Add labels via the sidebar or gh pr edit 2326 --add-label <label>

[huizzhan]

Hi @valarLip, this PR is to support optimized fused split GDR decode HIP implementation for Linear Attention project, please review, thanks for your support!

[yiijin]

please update the hip perf in the Test Result Table

[huizzhan]

please update the hip perf in the Test Result Table

Updated, please review, thanks~