arm64: dts: cavium: move non-MMIO node out of soc

Non-MMIO devices, which are BTW not really part of the SoC, should not
be within simple-bus, as reported by dtc W=1 warning:

  thunder-88xx.dtsi:374.28-379.5: Warning (simple_bus_reg): /soc/refclk50mhz: missing or empty reg/ranges property
Signed-off-by: Krzysztof Kozlowski <krzk@kernel.org>
Link: https://lore.kernel.org/r/20240402194129.69481-1-krzk@kernel.org

arch/arm64/boot/dts/cavium/thunder-88xx.dtsi

@@ -365,19 +365,19 @@ pmu {
 		interrupts = <1 7 4>;
 	};
 
+	refclk50mhz: refclk50mhz {
+		compatible = "fixed-clock";
+		#clock-cells = <0>;
+		clock-frequency = <50000000>;
+		clock-output-names = "refclk50mhz";
+	};
+
 	soc {
 		compatible = "simple-bus";
 		#address-cells = <2>;
 		#size-cells = <2>;
 		ranges;
 
-		refclk50mhz: refclk50mhz {
-			compatible = "fixed-clock";
-			#clock-cells = <0>;
-			clock-frequency = <50000000>;
-			clock-output-names = "refclk50mhz";
-		};
-
 		gic0: interrupt-controller@8010,00000000 {
 			compatible = "arm,gic-v3";
 			#interrupt-cells = <3>;