Help: Update CUDA_ARCHITECTURES docs for generic all/all-major support

Since commit 8f64df0a7c (CUDA: Generic all and all-major support,
2021-12-19, v3.23.0-rc1~23^2), these special values do not require any
specific compiler or version.

While at it, re-organize CUDA_ARCHITECTURES special value documentation.
Move the `versionadded` markup inside each special value so we can add
more in future versions.