rockchip: board: evb_rk3399: initialize pwm0 for dispaly backlight

Enable pwm0 for display of rk3399 evb board. The PWM do not have decicated
interrupt number in dts and can not get periph_id by pinctrl framework. So
init them here.
Signed-off-by: NEric Gao <eric.gao@rock-chips.com>
Reviewed-by: NSimon Glass <sjg@chromium.org>

board/rockchip/evb_rk3399/evb-rk3399.c

@@ -29,6 +29,13 @@ int board_init(void)
 		goto out;
 	}
 
+	/* Enable pwm0 for panel backlight */
+	ret = pinctrl_request_noflags(pinctrl, PERIPH_ID_PWM0);
+	if (ret) {
+		debug("%s PWM0 pinctrl init fail! (ret=%d)\n", __func__, ret);
+		goto out;
+	}
+
 	ret = pinctrl_request_noflags(pinctrl, PERIPH_ID_PWM2);
 	if (ret) {
 		debug("%s PWM2 pinctrl init fail!\n", __func__);