librem5-evk: Keep backlight disabled by default

Signed-off-by: Guido Günther <guido.gunther@puri.sm>

arch/arm64/boot/dts/freescale/librem5-evk.dtsi

@@ -227,7 +227,7 @@
                 brightness-levels = <0 10 20 30 40 50 60 70 80 90>;
                 /* Default brightness level (index into the array defined by the "brightness-levels" property) */
                 default-brightness-level = <0>;
-                status = "okay";
+                status = "disabled";
         };
 };