ARM: dts: AM33XX: Add PWM backlight DT data to am335x-evmsk

PWM output from ecap2 uses as backlight source. Also adds low threshold
value to have a uniform divisions in brightness-levels scales with
inverse polarity.

Signed-off-by: Philip Avinash <avinashphilip@ti.com>
Reviewed-by: Thierry Reding <thierry.reding@avionic-design.de>
Signed-off-by: Sebastian Andrzej Siewior <bigeasy@linutronix.de>
Signed-off-by: Benoit Cousson <benoit.cousson@linaro.org>

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

@@ -71,6 +71,12 @@
 				0x1b4 (PIN_OUTPUT_PULLDOWN | MUX_MODE3)		/* xdma_event_intr1.clkout2 */
 			>;
 		};
+
+		ecap2_pins: backlight_pins {
+			pinctrl-single,pins = <
+				0x19c 0x4	/* mcasp0_ahclkr.ecap2_in_pwm2_out MODE4 */
+			>;
+		};
 	};
 
 	ocp {
@@ -120,6 +126,16 @@
 				st,max-limit-z = <750>;
 			};
 		};
+
+		epwmss2: epwmss@48304000 {
+			status = "okay";
+
+			ecap2: ecap@48304100 {
+				status = "okay";
+				pinctrl-names = "default";
+				pinctrl-0 = <&ecap2_pins>;
+			};
+		};
 	};
 
 	vbat: fixedregulator@0 {
@@ -199,6 +215,13 @@
 			gpios = <&gpio2 5 GPIO_ACTIVE_HIGH>;
 		};
 	};
+
+	backlight {
+		compatible = "pwm-backlight";
+		pwms = <&ecap2 0 50000 1>;
+		brightness-levels = <0 58 61 66 75 90 125 170 255>;
+		default-brightness-level = <8>;
+	};
 };
 
 #include "tps65910.dtsi"