mlir/lib/Dialect/GPU/Transforms: improve context management in SerializeToCubin (#65779)

This commit adjusts the CUDA context management in the SerializeToCubin
pass. In particular, it uses the device 0 primary context instead of
creating a new CUDA context on each invocation of SerializeToCubin. This
yields very large improvements in compile time, especially if an
application (like a JIT compiler) is calling SerializeToCubin
repeatedly.

Differential Revision: https://reviews.llvm.org/D159487



Co-authored-by: Rohan Yadav <rohany@cs.stanford.edu>