Remove gpu-arch pages, link to ROCm docs instead

[neon60]

Motivation

The GPU architecture documentation is now maintained in the ROCm repository. Delete the superseded instinct-docs pages and images, and repoint the TOC and landing-page cards to the ROCm-hosted page.

Technical Details

The ROCm version at docs/reference/gpu-arch/ fully supersedes the instinct-docs pages: it adds complete MI350 content and a new mi350-performance-counters.rst, updates product naming ("GPUs" over "accelerators", "Series" capitalization), and fixes the performance-counters cross-reference to point at ROCprofiler-SDK instead of the deprecated ROCProfiler v1.

Changes in this PR:

• Deleted the superseded pages: docs/gpu-arch/{gpu-arch,mi100,mi250,mi300,mi350}.md and docs/gpu-arch/mi300-mi200-performance-counters.rst.
• Deleted the associated images: docs/images/gpu-arch/ (image001–008.png, mi300-node-level-arch.png), used only by the deleted pages.
• Repointed all three references to https://rocm.docs.amd.com/en/latest/reference/gpu-arch/index.html:
  • docs/sphinx/_toc.yml.in — replaced the full "Instinct Micro-architecture" subtree (including the per-generation ISA and white-paper PDF links) with a single external link entry.
  • docs/index.md — landing-page card.
  • docs/resources/common-reference.md — reference card.

Note: the per-generation ISA and white-paper PDF links previously surfaced in the TOC now live only on the ROCm page, which is the intended consolidation.

Test Plan

• Verify the build succeeds with no broken cross-references or missing-image warnings.
• Confirm no remaining references to the deleted docs/gpu-arch/* pages in the docs source.
• Verify the "Instinct Micro-architecture" entry in the TOC and both landing-page cards link to the ROCm-hosted page.

Test Result

• grep for gpu-arch/(gpu-arch|mi100|mi250|mi300|mi350) under docs/ returns no matches — no dangling references remain.

Submission Checklist

• Look over the contributing guidelines at https://github.com/ROCm/ROCm/blob/develop/CONTRIBUTING.md#pull-requests.

[AMD-melliott]

lgtm!