ARM: mxs: Add backlight support for M28EVK

This patch adds backlight support for M28EVK.
Signed-off-by: Marek Vasut <marex@denx.de>
Signed-off-by: Shawn Guo <shawn.guo@linaro.org>

arch/arm/boot/dts/imx28-m28evk.dts

@@ -235,6 +235,12 @@ auart2: serial@8006e000 {
 				pinctrl-0 = <&auart2_2pins_b>;
 				status = "okay";
 			};
+
+			pwm: pwm@80064000 {
+				pinctrl-names = "default";
+				pinctrl-0 = <&pwm4_pins_a>;
+				status = "okay";
+			};
 		};
 	};
 
@@ -270,6 +276,13 @@ mac1: ethernet@800f4000 {
 		};
 	};
 
+	backlight {
+		compatible = "pwm-backlight";
+		pwms = <&pwm 4 5000000>;
+		brightness-levels = <0 4 8 16 32 64 128 255>;
+		default-brightness-level = <6>;
+	};
+
 	regulators {
 		compatible = "simple-bus";