Refresh GB200 and GB300 GMC deployment guidance

[Prgolan28]

Summary

• Refresh GB200 GMC creation guidance from the GB200 / GB200-v2 and GB200-v3 Asset Handover Documents updated June 25, 2026.
• Refresh GB300 GMC creation guidance from the GB300 Single Plane and Multiplanar Asset Handover Documents updated June 25, 2026.
• Replace stale available-host-count / --size creation guidance with targetSize-based gpu-memory-cluster-scale-config examples.
• Correct the GMC delete placeholder OCID type and add a GB300 post-launch topology metadata check for single-plane vs multiplanar hosts.

Source documents

• BM.GPU.GB200.4 and BM.GPU.GB200-v2 Asset Handover Document: https://confluence.oraclecorp.com/confluence/pages/viewpage.action?pageId=16922529465
• BM.GPU.GB200-v3.4 Asset Handover Document: https://confluence.oraclecorp.com/confluence/pages/viewpage.action?pageId=18482799924
• BM.GPU.GB300.4 Single Plane Asset Handover Document: https://confluence.oraclecorp.com/confluence/pages/viewpage.action?pageId=20647441123
• BM.GPU.GB300.4 Multiplanar Asset Handover Document: https://confluence.oraclecorp.com/confluence/pages/viewpage.action?pageId=20647437510

Validation

• Compared current README coverage across the GPU AHD set and OCI OS Images page.
• Ran git diff --check.
• No credentials were copied or created.

Note: This PR is intentionally separate from #12, which adds the distinct GB300 Multiplanar README variant.

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[amgowda-oci]

I dont see any OS image and or driver changes for these GB docs neither Mi355X etc. Can you check again?