arm64: dts: rockchip: add backlight support for rk3399 evb board

Add backlight node for evb board, perpare for panel device node.
Signed-off-by: Yakir Yang <ykk@rock-chips.com>
Signed-off-by: Caesar Wang <wxt@rock-chips.com>
Signed-off-by: Heiko Stuebner <heiko@sntech.de>

arch/arm64/boot/dts/rockchip/rk3399-evb.dts

@@ -49,6 +49,46 @@ / {
 	compatible = "rockchip,rk3399-evb", "rockchip,rk3399",
 		     "google,rk3399evb-rev2";
 
+	backlight: backlight {
+		compatible = "pwm-backlight";
+		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  99 100 101 102 103
+			104 105 106 107 108 109 110 111
+			112 113 114 115 116 117 118 119
+			120 121 122 123 124 125 126 127
+			128 129 130 131 132 133 134 135
+			136 137 138 139 140 141 142 143
+			144 145 146 147 148 149 150 151
+			152 153 154 155 156 157 158 159
+			160 161 162 163 164 165 166 167
+			168 169 170 171 172 173 174 175
+			176 177 178 179 180 181 182 183
+			184 185 186 187 188 189 190 191
+			192 193 194 195 196 197 198 199
+			200 201 202 203 204 205 206 207
+			208 209 210 211 212 213 214 215
+			216 217 218 219 220 221 222 223
+			224 225 226 227 228 229 230 231
+			232 233 234 235 236 237 238 239
+			240 241 242 243 244 245 246 247
+			248 249 250 251 252 253 254 255>;
+		default-brightness-level = <200>;
+		enable-gpios = <&gpio1 13 GPIO_ACTIVE_HIGH>;
+		pwms = <&pwm0 0 25000 0>;
+	};
+
 	clkin_gmac: external-gmac-clock {
 		compatible = "fixed-clock";
 		clock-frequency = <125000000>;