For compiling models, we don't really need a context for a real device.
To support ML frameworks models in which compilation happens
ahead-of-time (AoT), add API for compilation that doesn't require a
pipe_context.
Add struct pipe_ml_device with function pointers for:
- ml_operation_supported: query operation support
- ml_subgraph_create: compile a subgraph
- ml_subgraph_serialize: serialize a compiled subgraph
- ml_subgraph_destroy: free subgraph resources
Move ml_operation_supported, ml_subgraph_create, and
ml_subgraph_destroy from pipe_context to pipe_ml_device.
Add pipe_screen::get_ml_device() to obtain the device.
Change pipe_ml_subgraph.context (pipe_context*) to
pipe_ml_subgraph.device (pipe_ml_device*).
Part-of: <https://gitlab.freedesktop.org/mesa/mesa/-/merge_requests/40167>