This adds a DRM/KMS based backend to the system, as per #42. This system finds a CRTC and a connector, then uses that to create a frame buffer and a DUMB buffer that it can render to.
There's much more to do, and is left as an exercise for anyone with a significant DRM-based use case to pick up and fix.
Signed-off-by: John Nunley <dev@notgull.net>