Claude review: drm/panthor: Lazily allocate pages on mmap()

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

Patch Review

Good refactoring of the fault handler into non-blocking/blocking paths.

One concern: In `panthor_gem_any_fault`, when `fault_flag_allow_retry_first` is true and `FAULT_FLAG_RETRY_NOWAIT` is not set, the code does:
```c
drm_gem_object_get(&bo->base);
mmap_read_unlock(vmf->vma->vm_mm);
ret = blocking_page_setup(vmf, order, bo, page_offset, false);
drm_gem_object_put(&bo->base);
return ret;
```
This correctly grabs a reference before releasing the mmap lock. In `blocking_page_setup` with `mmap_lock_held=false`, on error, it returns `VM_FAULT_RETRY` rather than `VM_FAULT_SIGBUS`, which is correct since the mmap lock isn't held.

No issues.

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