ARM: dts: am335x-evmsk: Add phandle for the backlight for the panel

With the backlight phandle the driver can manage the backlight on/off in
sync with the panel enable/disable.
Signed-off-by: Peter Ujfalusi <peter.ujfalusi@ti.com>
Signed-off-by: Tony Lindgren <tony@atomide.com>

arch/arm/boot/dts/am335x-evmsk.dts

@@ -137,7 +137,7 @@ switch4 {
 		};
 	};
 
-	backlight {
+	lcd_bl: backlight {
 		compatible = "pwm-backlight";
 		pwms = <&ecap2 0 50000 PWM_POLARITY_INVERTED>;
 		brightness-levels = <0 58 61 66 75 90 125 170 255>;
@@ -172,6 +172,7 @@ panel {
 		pinctrl-names = "default", "sleep";
 		pinctrl-0 = <&lcd_pins_default>;
 		pinctrl-1 = <&lcd_pins_sleep>;
+		backlight = <&lcd_bl>;
 		status = "okay";
 		panel-info {
 			ac-bias		= <255>;