drm/panel: nt36672a: add backlight support

Add support for backlight. This panel supports backlight control
through the QCOM WLED driver in Xiaomi Poco F1 device.
Signed-off-by: Joel Selvaraj <jo@jsfamily.in>
Reviewed-by: Marijn Suijten <marijn.suijten@somainline.org>
Signed-off-by: Sumit Semwal <sumit.semwal@linaro.org>
Link: https://patchwork.freedesktop.org/patch/msgid/BY5PR02MB700935F5817128CB7C3991CDD9E09@BY5PR02MB7009.namprd02.prod.outlook.com

drivers/gpu/drm/panel/panel-novatek-nt36672a.c

@@ -628,6 +628,10 @@ static int nt36672a_panel_add(struct nt36672a_panel *pinfo)
 
 	drm_panel_init(&pinfo->base, dev, &panel_funcs, DRM_MODE_CONNECTOR_DSI);
 
+	ret = drm_panel_of_backlight(&pinfo->base);
+	if (ret)
+		return dev_err_probe(dev, ret, "Failed to get backlight\n");
+
 	drm_panel_add(&pinfo->base);
 
 	return 0;