[Bugfix][CPU] Fix broken AVX2 CPU TP support

[Isotr0py]

FIX #16800 (link existing issues this PR will resolve)

[rank0]: AttributeError: '_OpNamespace' '_C' object has no attribute 'init_shm_manager'

• Add native torch.distributed fallback for AVX2 CPU, since _CPUSHMDistributed are only available for AVX512 CPU.

[github-actions]

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