docs: update NVLink partitioning docs after removal of NMX-M

[tmcroberts97]

How would you describe the priority of this documentation request

High

Please provide a link or source to the relevant docs

https://github.com/NVIDIA/infra-controller/blob/main/docs/manuals/nvlink_partitioning.md

Describe the problems in the documentation

Update the NVLink partitioning docs to reflect that NMX-M integration has been removed, and replaced with direct NMX-C calls.

(Optional) Propose a correction

No response

Code of Conduct

• I agree to follow NCX Infra Controller's Code of Conduct
• I have searched the open documentation issues and have found no duplicates for this documentation issue

[mxh-0xbb]

Documentation rollout should be aligned with code release.