Tracking issue for MCP 965: For `nvptx64`, drop old CPUs and ISAs - drop support for `target-cpu` < SM 7.0 and PTX ISA < 7.0

This is a tracking issue for MCP "For nvptx64, drop old CPUs and ISAs - drop support for target-cpu < SM 7.0 and PTX ISA < 7.0" (rust-lang/compiler-team#965).

[!NOTE]
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Steps

• Implement the MCP
• Adjust documentation
  • In the Rust Compiler Development Guide if applicable (e.g., for refactorings)
  • In the Rust Forge if applicable (e.g., for policy changes)
  • In the rustc book if applicable (e.g., for target tier or CLI changes)

Unresolved questions

None so far.

Implementation history

Empty so far.

@kjetilkjeka, consider @rustbot claim'ing the work.

Start with MCP rust-lang/compiler-team#965 and the Rust Compiler Development Guide, Rust Forge, and rustc book links named in the checklist. Done means the MCP is implemented and any applicable documentation updates are completed; no implementation files or tests are identified here.