gpu: drm: adp: Allow max brightness to be set via device tree

The max brightness between different summit panels may be different
so allow the max brightness to be set via device tree.

Tested-by: Sasha Finkelstein <fnkl.kernel@gmail.com>
Signed-off-by: Nick Chan <towinchenmi@gmail.com>

Author: asdfugil

drivers/gpu/drm/adp/panel-summit.c

@@ -46,7 +46,11 @@ static int summit_probe(struct mipi_dsi_device *dsi)
 
 	mipi_dsi_set_drvdata(dsi, panel);
 	panel->dsi = dsi;
-	props.max_brightness = 255;
+
+	int ret = device_property_read_u32(dev, "max-brightness", &props.max_brightness);
+
+	if (ret)
+		props.max_brightness = 255;
 	props.type = BACKLIGHT_RAW;
 
 	panel->bl = devm_backlight_device_register(dev, dev_name(dev),