Add is_cpu op

[kiya00]

Before submitting

• Was this discussed/approved via a Github issue? (no need for typos and docs improvements)
• Did you read the contributor guideline, Pull Request section?
• Did you make sure to update the docs?
• Did you write any new necessary tests?

What does this PR do?

It's used in GPT-OSS transformer implementation

# File: /sgl-workspace/sglang/python/sglang/srt/distributed/parallel_state.py:562 in all_reduce, code: if input_.is_cpu:
getattr_1 = output_parallel.is_cpu;  getattr_1 = None

[mattteochen]

Thanks @kiya00 !

[shino16]

Thank you, it looks good to me aside from @kshitij12345's review.

[kiya00]

Hi @KaelanDt , could you help review it, it's ready to merge

[KaelanDt]

thank you @kiya00