Claude review: gpu: nova-core: gsp: make `Cmdq` a pinned type

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

Patch Review

**Status: Looks good**

A clean mechanical change to make `Cmdq` pin-initialized, required for the `Mutex` in patch 4.

Adding `#[pin_data]` and `#[pin]`:
```rust
+#[pin_data]
 pub(crate) struct Cmdq {
     ...
```

Changing the constructor from `Result<Cmdq>` to `impl PinInit<Self, Error>`:
```rust
-    pub(crate) fn new(dev: &device::Device<device::Bound>) -> Result<Cmdq> {
-        let gsp_mem = DmaGspMem::new(dev)?;
-        Ok(Cmdq {
+    pub(crate) fn new(dev: &device::Device<device::Bound>) -> impl PinInit<Self, Error> + '_ {
+        try_pin_init!(Self {
+            gsp_mem: DmaGspMem::new(dev)?,
             dev: dev.into(),
             seq: 0,
-            gsp_mem,
         })
```

Updating the caller in `gsp.rs` to use pin-init syntax:
```rust
-                cmdq: Cmdq::new(dev)?,
+                cmdq <- Cmdq::new(dev),
```

And the reference change since `cmdq` is now behind a pin:
```rust
-                    dma_write!(rmargs[0].inner = fw::GspArgumentsCached::new(cmdq))?;
+                    dma_write!(rmargs[0].inner = fw::GspArgumentsCached::new(&cmdq))?;
```

No issues. Already has Reviewed-by from Zhi Wang.

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