Claude review: gpu: nova-core: switch to kernel bitfield macro

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

Patch Review

**Review: Clean migration, looks good**

This is a straightforward consumer migration from the local `bitfield!` to `kernel::bitfield!`.

**API migration:** The key changes are:
- `as u8` field type annotations removed (replaced by `Bounded`-based generic inference)
- `set_major(...)` → `with_major(...)` (naming convention change)
- `Self::default()` → `Self::zeroed()` (since new macro doesn't generate `Default`)
- `#[macro_use] mod bitfield;` → `use kernel::bitfield;`

**Functional equivalence verified:** The `MsgHeaderVersion` previously used:
```rust
Self::default()
    .set_major(Self::MAJOR_TOT)
    .set_minor(Self::MINOR_TOT)
```
Now:
```rust
Self::zeroed()
    .with_major(Self::MAJOR_TOT)
    .with_minor(Self::MINOR_TOT)
```
Since `MAJOR_TOT: u8 = 3` and `MINOR_TOT: u8 = 0`, and the fields are 8-bit (31:24 and 23:16 respectively), the `u8` values will implicitly convert via `From<u8> for Bounded<u32, 8>`. The `zeroed()` and `default()` both produce all-zero storage for integer-backed types, so this is functionally identical.

**Import cleanup:** The diff includes a minor reformatting of `use kernel::sizes::{SZ_128K, SZ_1M}` which is just the `//` comment marker moving between lines -- likely a rustfmt artifact. This is harmless.

**329-line deletion:** The entire `drivers/gpu/nova-core/bitfield.rs` file is removed, which was the local implementation. This is the expected cleanup.

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Generated by Claude Code Patch Reviewer