Claude review: media: iris: retrieve UBWC platform configuration

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

Patch Review

This patch adds the `QCOM_UBWC_CONFIG` Kconfig dependency, a forward declaration of `struct qcom_ubwc_cfg_data` in `iris_core.h`, and retrieves the config at probe time.

The implementation is straightforward and correct:

```c
core->ubwc_cfg = qcom_ubwc_config_get_data();
if (IS_ERR(core->ubwc_cfg))
    return PTR_ERR(core->ubwc_cfg);
```

**Minor nit:** Modern kernel probe functions prefer `dev_err_probe()` for error handling, which silences `EPROBE_DEFER` noise and provides a consistent error message for genuine failures:

```c
if (IS_ERR(core->ubwc_cfg))
    return dev_err_probe(core->dev, PTR_ERR(core->ubwc_cfg),
                         "failed to get UBWC config\n");
```

The `select QCOM_UBWC_CONFIG` in Kconfig ensures the real implementation is compiled in, avoiding the stub that always returns `-EOPNOTSUPP`.

No other issues.

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