librem5-evk: Use a percent scaled brightness

This allows for smother dimming.
Signed-off-by: Guido Günther <guido.gunther@puri.sm>

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

@@ -17,7 +17,7 @@
 #include "librem5-evk.dtsi"
 
 &backlight_dsi {
-	default-brightness-level = <3>;
+	default-brightness-level = <40>;
 	status = "okay";
 };
 

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

@@ -224,7 +224,17 @@
                 compatible = "pwm-backlight";
                 /* 200 Hz for the PAM2841 */
                 pwms = <&pwm1 0 5000000>;
-                brightness-levels = <0 10 20 30 40 50 60 70 80 90>;
+                brightness-levels = < 0  1  2  3  4  5  6  7  8  9
+                                     10 11 12 13 14 15 16 17 18 19
+                                     20 21 22 23 24 25 26 27 28 29
+                                     30 31 32 33 34 35 36 37 38 39
+                                     40 41 42 43 44 45 46 47 48 49
+                                     50 51 52 53 54 55 56 57 58 59
+                                     60 61 62 63 64 65 66 67 68 69
+                                     70 71 72 73 74 75 76 77 78 79
+                                     80 81 82 83 84 85 86 87 88 89
+                                     90 91 92 93 94 95 96 97 98 99
+                                    100>;
                 /* Default brightness level (index into the array defined by the "brightness-levels" property) */
                 default-brightness-level = <0>;
                 status = "disabled";