[NVPTX] Do not addrspacecast AS-specific kernel arguments.

Fixes https://github.com/llvm/llvm-project/issues/46954

The assumption that generic pointers passed to a CUDA kernel is CUDA-specific
and should not be applied to non-CUDA compilations.  Addrspacecasts to global AS
and back should never be applied to AS-specific pointers.

In order to make tests actually do the testing for non-CUDA compilation, we need
to get TargetMachine from the TargetPassConfig, instead of passing it explicitly
as a pass constructor argument.

Differential Revision: https://reviews.llvm.org/D142581