Claude review: drm: nova: demonstrate interaction with nova-core

[Claude Code Review Bot <claude-review@example.com>]

Patch Review

**Status: POC, not for merging — design is sound but has review-worthy patterns**

This demonstrates the end-to-end flow: nova-core exports an `AuxData` struct containing GPU information, and nova-drm retrieves it during probe.

**Field reordering for drop safety** is the most important change:

```rust
pub struct NovaCore<'bound> {
    _reg: auxiliary::Registration<'bound, ForLt!(AuxData<'_>)>,
    #[pin]
    pub(crate) gpu: Gpu<'bound>,
    bar: pci::Bar<'bound, BAR0_SIZE>,
}
```

Rust drops fields in declaration order, so `_reg` drops first (unregistering the auxiliary device and releasing the `AuxData` reference to `gpu`), then `gpu`, then `bar`. This is correct and the comment documenting the invariant is helpful.

**Initialization order** uses `try_pin_init!(&this in NovaCore { bar: ..., gpu <- ..., _reg: ... })` which initializes in *macro invocation order* (bar → gpu → _reg), not declaration order. This is correct: bar must exist before gpu (which references it), and gpu must exist before _reg (which stores a reference to it via AuxData).

**Unsafe self-referential pointer:**

```rust
gpu: &*core::ptr::from_ref(&this.as_ref().gpu),
```

This creates a reference from the `AuxData` to the in-place-initialized `gpu` field. The safety argument (pinned, stable address, dropped in correct order) is sound and follows the established pattern visible in `scatterlist.rs` and elsewhere in the kernel.

**Visibility changes** (`pub mod driver`, `pub mod gpu`, `pub(crate) chipset` → `pub(crate) chipset` on Spec field, `pub enum Chipset`) are necessary for cross-crate access. In a real implementation, you'd likely want a more controlled public API rather than exposing internal fields with `pub(crate)` on `Spec.chipset` and `Gpu.spec` — but for a POC this is fine.

**Minor note:** The `#[allow(missing_docs)]` on the `Chipset` enum and the added `//!` module docs are just to satisfy Clippy for public items, as noted in the commit message.

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