nouveau: move GSP headers to a generated header file.

When Ben originally wrote the GSP port, he hand crafted/copied a bunch
of structures and defines from NVIDIA's open-gpu-kernel-modules.

I recently wrote a libclang based parser in rust that parsers the
complete opengpu repo and writes out useful info into 2 json files.

1 file is suitable for generating a memory mapped structure format
the other is good for generate C headers and types.

The parser is https://github.com/airlied/gsp-parse

 but will probably
move somewhere nicer.

This uses the generator to create gen.h which is a single header file
that requires one manual fixup to add back a __counted_by that was added
downstream but not upstream.

Signed-off-by: Dave Airlie <airlied@redhat.com>