dts: arm: nordic: Define power states for nrf54h20/cpuapp

Add definition of low power states 'idle' and 's2ram'
for nrf54h20/cpuapp.

Signed-off-by: Sebastian Głąb <sebastian.glab@nordicsemi.no>

dts/arm/nordic/nrf54h20_cpuapp.dtsi

@@ -59,3 +59,23 @@ wdt011: &cpuapp_wdt011 {};
 &grtc {
 	interrupts = <109 NRF_DEFAULT_IRQ_PRIORITY>;
 };
+
+/ {
+	power-states {
+		idle: idle {
+			compatible = "zephyr,power-state";
+			power-state-name = "suspend-to-idle";
+			min-residency-us = <100000>;
+		};
+
+		s2ram: s2ram {
+			compatible = "zephyr,power-state";
+			power-state-name = "suspend-to-ram";
+			min-residency-us = <800000>;
+		};
+	};
+};
+
+&cpu {
+	cpu-power-states = <&idle &s2ram>;
+};