[llvm] [mlir] [mlir][gpu] Change GPU modules to globals (PR #135478)

[Valentin Clement バレンタイン クレメン via llvm-commits]

clementval wrote:

> Moreover, the ops have clear low level meaning, thus they have direct translation, so I don't see any benefit in handling them during conversion.

I agree with this statement but for me the loading/unloading of the module should be delegated to another operation that has this clear meaning so it would be more modular. 

https://github.com/llvm/llvm-project/pull/135478