riscv: sophgo: dts: add pwm-fan for Milk-V Pioneer

Milk-V Pioneer uses fan as cooling-device, and speed of the fan is
controlled by the first channel of pwm controller of SG2042.

Signed-off-by: Chen Wang <unicorn_wang@outlook.com>
Link: https://lore.kernel.org/r/dd23362328f77dd91aa9354848bbb0abad0f554b.1739351437.git.unicorn_wang@outlook.com
Signed-off-by: Inochi Amaoto <inochiama@gmail.com>

Author: unicornx

arch/riscv/boot/dts/sophgo/sg2042-milkv-pioneer.dts

@@ -73,6 +73,13 @@
 };
 
 / {
+	pwmfan: pwm-fan {
+		compatible = "pwm-fan";
+		cooling-levels = <103 128 179 230 255>;
+		pwms = <&pwm 0 40000 0>;
+		#cooling-cells = <2>;
+	};
+
 	thermal-zones {
 		soc-thermal {
 			polling-delay-passive = <1000>;