dts: exynos54xx: Add samsung, pwm-out-gpio property to FIMD node

Now that the exynos_fb driver supports handling backlight GPIO
via DT, specify pwm output property via FIMD DT node.

Signed-off-by: Ajay Kumar <ajaykumar.rs@samsung.com>
Reviewed-by: Simon Glass <sjg@chromium.org>
Tested-by: Simon Glass <sjg@chromium.org>
Signed-off-by: Minkyu Kang <mk7.kang@samsung.com>

arch/arm/dts/exynos54xx.dtsi

@@ -168,6 +168,7 @@
 	fimd@14400000 {
 		/* sysmmu is not used in U-Boot */
 		samsung,disable-sysmmu;
+		samsung,pwm-out-gpio = <&gpb2 0 GPIO_ACTIVE_HIGH>;
 	};
 
 	dp@145b0000 {