asahi: Linux UAPI prep work

Let's get us ready for the upcoming explicit sync Linux UAPI, even though it's not stable yet, to reduce the delta downstream.

First drop macOS support, which has run its course. Next time we need it we can reimplement it as a shim layer on top of the UAPI definitions, which will be much cleaner.

Then add the device scaffolding we have downstream for the new UAPI, except with all the UAPI calls stubbed out. This includes things like VMA management (for a userspace VM management world), as well as all the wrappers for generic ioctls which are not driver-specific.

Finally, implement the batch tracking changes required for the driver to work in an explicit sync world. The vast majority of this deals with sync objects and DMA-BUF fence import/export, so it does not actually depend on the driver UAPI.