Claude review: drm/bridge: Add out-of-band HPD notify handler

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

Patch Review

Adds a new `oob_notify` callback to `struct drm_bridge_funcs` and calls it from `drm_bridge_connector_oob_hotplug_event()` for every bridge in the chain.

```c
+	void (*oob_notify)(struct drm_bridge *bridge,
+			   struct drm_connector *connector,
+			   enum drm_connector_status status);
```

**Design question (acknowledged by author):** The cover letter mentions this might not be the ideal solution. The concern is valid — `oob_hotplug_event` already calls `drm_bridge_connector_handle_hpd()` which goes through `hpd_notify`. Having a separate `oob_notify` that fires before the existing `hpd_notify` flow creates two notification paths. The rationale (OOB needs to force HPD state before `.detect` runs) is sound, but this should be discussed with DRM bridge maintainers (Dmitry Baryshkov is already CC'd).

**Minor:** The iteration uses `drm_for_each_bridge_in_chain_scoped` which notifies *all* bridges, but only the DP controller bridge will actually implement `oob_notify`. This is fine — the callback check handles it.

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