[XPU] work around for sp, avoid custom op import error

[jikunshang]

Purpose

#27126 add import SequenceParallelismPass, which break xpu path. we should follow L16-L20, import only for cuda_alike platform.

Test Plan

CI.

Test Result

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• The purpose of the PR, such as "Fix some issue (link existing issues this PR will resolve)".
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[gemini-code-assist]

Code Review

This pull request addresses an import error for SequenceParallelismPass on non-CUDA platforms by making the import conditional. While this fixes the immediate issue, it introduces a potential runtime NameError if sequence parallelism is enabled on an unsupported platform. I've provided a suggestion to create a dummy pass for unsupported platforms, which makes the code more robust by preventing crashes and gracefully disabling the feature with a warning. This approach is more resilient to configuration errors.

[Yikun]

Thanks for fixing, we also validated this with vllm-ascend. This should also be backported to release/v0.11.1 branch

[ywang96]

Thanks for fixing, we also validated this with vllm-ascend. This should also be backported to release/v0.11.1 branch

Sounds good - will cherry pick there!