ARM: dts: r8a7791: Add APMU node

Add a DT node for the Advanced Power Management Units (APMU), and use
the enable-method to point out that the APMU should be used for SMP
support.
Signed-off-by: Magnus Damm <damm+renesas@opensource.se>
Signed-off-by: Geert Uytterhoeven <geert+renesas@glider.be>
Signed-off-by: Simon Horman <horms+renesas@verge.net.au>

arch/arm/boot/dts/r8a7791.dtsi

@@ -43,6 +43,7 @@ aliases {
 	cpus {
 		#address-cells = <1>;
 		#size-cells = <0>;
+		enable-method = "renesas,apmu";
 
 		cpu0: cpu@0 {
 			device_type = "cpu";
@@ -101,6 +102,12 @@ cooling-maps {
 		};
 	};
 
+	apmu@e6152000 {
+		compatible = "renesas,r8a7791-apmu", "renesas,apmu";
+		reg = <0 0xe6152000 0 0x188>;
+		cpus = <&cpu0 &cpu1>;
+	};
+
 	gic: interrupt-controller@f1001000 {
 		compatible = "arm,gic-400";
 		#interrupt-cells = <3>;