The initial posting of the Apple AGX graphics driver

Asahi Lina has posted aninitial version of a Rust-based driver for Apple AGX graphicsprocessors; the posting includes a fair amount of Rust infrastructure forgraphics drivers in general.

While developing the driver, I tried to make use of Rust's safetyand lifetime features to provide not just CPU-side safety, but alsopartial firmware-ABI safety. Thanks to this, it has turned out tobe a very stable driver even though GPU firmware crashes are fatal(no restart capability, need to reboot!) and the FW/driverinterface is a huge mess of unsafe shared memory structures withcomplex pointer chains.