Claude review: drm/v3d: Remove dedicated fence_lock

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

Patch Review

With `queue_lock` no longer taken from the IRQ handler for stats updates (the original reason for the split), merging `fence_lock` back is a reasonable simplification:

```c
dma_fence_init(&fence->base, &v3d_fence_ops, &queue->queue_lock,
	       queue->fence_context, fence->seqno);
```

The reasoning in the commit message is sound. The `fence_lock` was introduced specifically because `v3d_job_update_stats` was taking `queue_lock` in the IRQ handler alongside DMA fence signaling, which caused PREEMPT_RT issues. That usage is now gone.

One thing worth verifying: after this merge, `queue_lock` is used from process context with `spin_lock_irqsave` (e.g., in `v3d_bin_job_run`) and from IRQ context via `dma_fence_signal`. Since both paths use IRQ-safe locking, this is correct for non-RT kernels. On PREEMPT_RT, the situation is the same as the original `fence_lock` (both were `spinlock_t`), so no regression there.

Clean and correct patch.

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