NV04/NV10 load_context()/save_context() are stubs. I don't know enough about
how they work to implement them sanely. The "old" context_switch() code
remains hooked up, so it shouldn't break anything.
NV20 will probably break if load_context() works. No inital context values
are filled in, so when the first channel is created PGRAPH will probably end
up having its state zeroed. Some setup from nv20_graph_init() will probably
need to be moved to the per-channel context setup.
The PGRAPH init for the various cards will need cleaning up at some point,
a lot of the values written there are per-context state left over from the
all the hardcoding done in the ddx.
It's possible some cards get broken by this commit, let me know.
Tested on: NV5, NV18, NV28, NV35, NV40, NV4E