Support for driver-specific APIs

[zigazeljko]

I am currently trying to do some low-level GPU programming (for Nvidia cards using the open-source nouveau driver) and so, I need access to driver-specific APIs for managing buffers and executing command lists.

It seems I'm not the only one needing this, since there are already other projects using this crate (eg. rudihorn/drm-vc4-grabber) that implement their own bindings for driver-specific APIs, so it would make sense to unify them under this crate.

Is this considered to be in-scope for this crate? If so, I would be happy to contribute to this crate.

[Drakulix]

The original scope of this project was writing libdrm bindings, which has then turned into some abstraction over drm-related ioctls. So I guess, this could be in scope now?

How stable are these driver-specific apis? I am not sure, if we want to pull them into the main crate, if those may frequently become out-of-date.

At the very least any PR is welcome that eases support for driver-specific APIs out-of-tree (like drm-vc4-grabber). But I think unifying may be a good idea, I am just not sure about the maintenance burden, that this puts onto drm-rs.