turnip: Add support for compute shaders.

turnip: Add support for compute shaders.

Since compute shares the FS state with graphics, we have to re-upload the
pipeline state when switching between compute dispatch and graphics draws.
We could potentially expose graphics and compute as separate queues and
then we wouldn't need pipeline state management, but the closed driver
exposes a single queue and consistency with them is probably good.

So far I'm emitting texture/ibo state as IBs that we jump to.  This is
kind of silly when we could just emit it directly in our CS, but that's a
refactor we can do later.

Reviewed-by: Jonathan Marek <jonathan@marek.ca>