Claude review: drm: renesas: rz-du: Make DU reset control optional for RZ/T2H support

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

Patch Review

**Status: Acceptable, minor concern.**

The change is a one-liner:

```c
-	rcrtc->rstc = devm_reset_control_get_shared(rcdu->dev, NULL);
+	rcrtc->rstc = devm_reset_control_get_optional_shared(rcdu->dev, NULL);
```

This is the right approach for RZ/T2H which has no reset line. However, `devm_reset_control_get_optional_shared()` returns `NULL` (not an error) when no reset is specified in DT. The existing callers `reset_control_deassert(rcrtc->rstc)` and `reset_control_assert(rcrtc->rstc)` (in `rzg2l_du_crtc_get` at ~line 190 and `rzg2l_du_crtc_put` at line 210) are safe because the reset control API accepts `NULL` and treats it as a no-op. So this is correct.

**Minor concern:** By making the reset universally optional in the driver, a misconfigured DT for RZ/G2L/G2UL (which *does* require a reset) would silently succeed at probe time rather than failing early. The DT binding schema should catch this, but the driver loses its own defensive check. This is an acceptable tradeoff given that the binding enforces `resets` for non-RZ/T2H SoCs, and Laurent has already reviewed this.

Has Reviewed-by from Laurent Pinchart.

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