dts: arm: st: stm32h5: relocate power-states node

Relocate the `power-states` node from under the `soc` node to
the `cpus` node, making it consistent with other STM32 SoC series.

This resolves the device-tree warning:
(simple_bus_reg): /soc/power-states: missing or empty reg/ranges property.

Signed-off-by: Pisit Sawangvonganan <pisit@ndrsolution.com>

dts/arm/st/h5/stm32h5.dtsi

@@ -39,6 +39,15 @@
 				reg = <0xe000ed90 0x40>;
 			};
 		};
+
+		power-states {
+			stop: state0 {
+				compatible = "zephyr,power-state";
+				power-state-name = "suspend-to-idle";
+				substate-id = <1>;
+				min-residency-us = <20>;
+			};
+		};
 	};
 
 	clocks {
@@ -137,15 +146,6 @@
 			status = "disabled";
 		};
 
-		power-states {
-			stop: state0 {
-				compatible = "zephyr,power-state";
-				power-state-name = "suspend-to-idle";
-				substate-id = <1>;
-				min-residency-us = <20>;
-			};
-		};
-
 		rcc: rcc@44020c00 {
 			compatible = "st,stm32u5-rcc";
 			clocks-controller;