drm/rockchip: rgb: add support rk3308 rgb

add support for rgb panel or rgb covert to other interface panel.

Change-Id: I190ce6e08d38f794ecabb863e0def5e74890f75a
Signed-off-by: Sandy Huang <hjc@rock-chips.com>

Documentation/devicetree/bindings/display/rockchip/rockchip-rgb.txt

@@ -5,6 +5,7 @@ Required properties:
 - compatible: matching the soc type:
 	- "rockchip,rv1108-rgb";
 	- "rockchip,rk3066-rgb";
+	- "rockchip,rk3308-rgb";
 
 Optional properties:
 - pinctrl-names: must contain a "lcdc" entry.

drivers/gpu/drm/rockchip/rockchip_rgb.c

@@ -149,6 +149,8 @@ static const struct of_device_id rockchip_rgb_dt_ids[] = {
 		.compatible = "rockchip,rv1108-rgb",
 	}, {
 		.compatible = "rockchip,rk3066-rgb",
+	}, {
+		.compatible = "rockchip,rk3308-rgb",
 	},
 	{}
 };