[llvm] [lit] Refactor available `ptxas` features (PR #154439)

[Alex MacLean via llvm-commits]

https://github.com/AlexMaclean commented:

This will be very useful. I've personally run afoul of issues with versions of ptxas not working with a given configuration with %ptxas-verify several times. I would consider tweaking the naming of these a little bit. I'd recommend that we remove the "v" in the ISA features and rename "32" -> "ptr32". I'd also lean towards using `()` or `{}` to represent these (i.e. `ptxas(sm_90)`, `ptxas(isa-8.4)`) but that is more a matter of personal taste so if you or others disagree I'm happy to leave as is.

https://github.com/llvm/llvm-project/pull/154439