WIP Rust modules for Intel GPUs.

Possibly outdated docs at https://itycodes.org/doc/intel_gpu/ .

Structure:
- `src/uapi`:
    low-level ioctl bindings
- `src/uapi/i915`
    low-level ioctl bindings specific to i915
- `src/gpu`
    low-level OOP wrapper around the ioctl bindings
- `src/gpu/i915`
    low-level OOP wrapper around the i915-specific ioctl bindings