[libomptarget][devicertl][nfc] Remove some cuda intrinsics, simplify

[libomptarget][devicertl][nfc] Remove some cuda intrinsics, simplify

Replace __popc, __ffs with clang intrinsics. Move kmpc_impl_min to only file
that uses it and replace template with explictly typed.

Reviewed By: jdoerfert

Differential Revision: https://reviews.llvm.org/D95060