[XPU] Enable sequence parallel support for XPU

[chaojun-zhang]

Test Plan

Test Result

Configuration	Command	Median latency
Enable  SP	vllm bench latency --model meta-llama/Llama-3.1-8B -tp 2 --compilation-config '{"pass_config": {"enable_sp": true, "sp_min_token_num": 256}}'	2.346s
Disable SP	vllm bench latency --model meta-llama/Llama-3.1-8B -tp 2	2.491s

UT :
pytest -s -v tests/compile/correctness_e2e/test_sequence_parallel.py
pytest -s -v pytest -s -v tests/compile/correctness_e2e/test_sequence_parallel.py

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• The purpose of the PR, such as "Fix some issue (link existing issues this PR will resolve)".
• The test plan, such as providing test command.
• The test results, such as pasting the results comparison before and after, or e2e results
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[gemini-code-assist]

Code Review

This pull request enables sequence parallelism tests on XPU platforms by updating pytest markers and generalizing device selection using current_platform.device_type and torch.accelerator. It also moves the SequenceParallelismPass import out of the CUDA-specific guard in the pass manager. Feedback indicates that moving this pass alone is insufficient, as RMSNormQuantFusionPass remains guarded but is required by the newly enabled XPU tests, which will likely result in a NameError.

[gemini-code-assist]

Moving SequenceParallelismPass out of the is_cuda_alike() guard is necessary to support it on XPU. However, RMSNormQuantFusionPass (currently at line 32) remains inside the guard. Since the XPU tests added in this PR (tests/compile/passes/distributed/test_sequence_parallelism.py) explicitly enable fuse_norm_quant, the PostGradPassManager.configure() method will raise a NameError on XPU platforms when it attempts to instantiate RMSNormQuantFusionPass.

Additionally, AsyncTPPass (line 39) is guarded by is_cuda(), which will cause a similar NameError if fuse_gemm_comms is enabled on XPU. You should move RMSNormQuantFusionPass out of the guard as well, and ensure AsyncTPPass is handled safely for XPU.

[mergify]

This pull request has merge conflicts that must be resolved before it can be
merged. Please rebase the PR, @chaojun-zhang.

https://docs.github.com/en/pull-requests/collaborating-with-pull-requests/working-with-forks/syncing-a-fork

[yma11]

@chaojun-zhang Any latency difference w/ and w/o this feature enabled? and also the case with asyncTP enabled.

[chaojun-zhang]

@chaojun-zhang Any latency difference w/ and w/o this feature enabled? and also the case with asyncTP enabled.

• For latency please refer to Test Result in PR description.
• We will have a separate draft PR for asyncTP