ARM: dts: rockchip: drop veyron's nonstandard 'backlight-boot-off'

This was used out-of-tree as a hack for resolving issues where some
systems expect the backlight to turn on automatically at boot, while
others expect to manage the backlight status via a DRM/panel driver.
Those issues have since been fixed upstream in pwm_bl.c without device
tree hacks, and so this un-documented property should no longer be
useful.
Signed-off-by: Brian Norris <briannorris@chromium.org>
Signed-off-by: Heiko Stuebner <heiko@sntech.de>

arch/arm/boot/dts/rk3288-veyron-chromebook.dtsi

@@ -92,7 +92,6 @@ backlight: backlight {
 			248 249 250 251 252 253 254 255>;
 		default-brightness-level = <128>;
 		enable-gpios = <&gpio7 RK_PA2 GPIO_ACTIVE_HIGH>;
-		backlight-boot-off;
 		pinctrl-names = "default";
 		pinctrl-0 = <&bl_en>;
 		pwms = <&pwm0 0 1000000 0>;