Claude review: drm/v3d: Hold v3d_stats references in each job

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

Patch Review

This is the key patch that eliminates the need for `queue_lock` in the stats update path. Each job now holds its own refcounted references to both client and global stats:

```c
job->client_stats = v3d_stats_get(v3d_priv->stats[queue]);
job->global_stats = v3d_stats_get(v3d->queue[queue].stats);
```

The critical simplification in `v3d_job_update_stats` is correct — the old code needed `queue_lock` and the `if (job->file_priv)` NULL check because stats were embedded in `v3d_file_priv` which could be freed. With refcounting, the stats outlive the fd:

```c
void
v3d_job_update_stats(struct v3d_job *job)
{
	u64 now = local_clock();

	preempt_disable();
	v3d_stats_update(job->client_stats, now);
	v3d_stats_update(job->global_stats, now);
	preempt_enable();
}
```

The refactoring of `v3d_job_start_stats` into `v3d_stats_start` + `v3d_job_start_stats` is clean and makes both functions independent of queue type, which is why the `enum v3d_queue` parameter can be dropped. All callers are updated consistently.

The `v3d_job_free` cleanup correctly puts both stats references before freeing the job. The placement after `v3d_perfmon_put` and before `kfree` is appropriate.

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Generated by Claude Code Patch Reviewer