arm64: tegra: Add PWM fan support on Jetson Xavier

Enable PWM4 in device tree and use it to drive the PWM fan on the Jetson
Xavier.
Signed-off-by: Thierry Reding <treding@nvidia.com>

arch/arm64/boot/dts/nvidia/tegra194-p2972-0000.dts

@@ -12,5 +12,14 @@ cbb {
 		sdhci@3400000 {
 			status = "okay";
 		};
+
+		pwm@c340000 {
+			status = "okay";
+		};
+	};
+
+	fan {
+		compatible = "pwm-fan";
+		pwms = <&pwm4 0 45334>;
 	};
 };