[mlir][gpu] Productize `test-lower-to-nvvm` as `gpu-lower-to-nvvm` (#75775)

The `test-lower-to-nvvm` pipeline serves as the common and proper
pipeline for nvvm+host compilation, and it's used across our CUDA
integration tests.

This PR updates the `test-lower-to-nvvm` pipeline to `gpu-lower-to-nvvm`
and moves it within `InitAllPasses.h`. The aim is to call it from
Python, also having a standardize compilation process for nvvm.