[DOC]: ptx instructions documentation should be on their own doc sections

[gonzalobg]

Is this a duplicate?

• I confirmed there appear to be no duplicate issues for this bug and that I agree to the Code of Conduct

Is this for new documentation, or an update to existing docs?

New

Describe the incorrect/future/missing documentation

The Extended API page provides only a glossary: https://nvidia.github.io/cccl/libcudacxx/extended_api.html

But it seems the PTX instruction documentation got accidentally added there.

If this is a correction, please provide a link to the incorrect documentation. If this is a new documentation request, please link to where you have looked.

No response