[llvm] [NVPTX] cleanup & canonicalize `mov` (PR #129344)

[Alex MacLean via llvm-commits]

https://github.com/AlexMaclean commented:

Seems like some nice cleanup. While you're at it it might be good to remove the redundant `r` since the only thing you can move a value into is a register. Also looks like there are some other mov instructions such as `MOV_ADDR` and `MOV_DEPOT_ADDR` which you could switch to using the `b` variant as well. 

https://github.com/llvm/llvm-project/pull/129344