riscv: dts: microchip: move sysctrlr out of soc bus

The MPFS system controller has no registers of its own, so move it out
of the soc node to avoid dtbs_check warnings:
arch/riscv/boot/dts/microchip/microchip-mpfs-icicle-kit.dtb: soc: syscontroller: {'compatible': ['microchip,mpfs-sys-controller'], 'mboxes': [[15, 0]], 'status': ['okay']} should not be valid under {'type': 'object'}
Reported-by: Palmer Dabbelt <palmer@rivosinc.com>
Suggested-by: Rob Herring <robh@kernel.org>
Fixes: 528a5b1f ("riscv: dts: microchip: add new peripherals to icicle kit device tree")
Reviewed-by: Heiko Stuebner <heiko@sntech.de>
Signed-off-by: Conor Dooley <conor.dooley@microchip.com>
Link: https://lore.kernel.org/r/20220509142610.128590-3-conor.dooley@microchip.comSigned-off-by: Palmer Dabbelt <palmer@rivosinc.com>

arch/riscv/boot/dts/microchip/microchip-mpfs.dtsi

@@ -146,6 +146,11 @@ refclk: mssrefclk {
 		#clock-cells = <0>;
 	};
 
+	syscontroller: syscontroller {
+		compatible = "microchip,mpfs-sys-controller";
+		mboxes = <&mbox 0>;
+	};
+
 	soc {
 		#address-cells = <2>;
 		#size-cells = <2>;
@@ -446,10 +451,5 @@ mbox: mailbox@37020000 {
 			#mbox-cells = <1>;
 			status = "disabled";
 		};
-
-		syscontroller: syscontroller {
-			compatible = "microchip,mpfs-sys-controller";
-			mboxes = <&mbox 0>;
-		};
 	};
 };