boards: arm: stm32l476 nucleo board has low power states

The low power states 0∕1∕2 are added to the stm32l476rg
nucleo board, with default min residency values.
The substate-id is mapping the same Zephyr power state.
They correspond to the stm32l476 low power stop0/1/2 modes.

Signed-off-by: Francois Ramu <francois.ramu@st.com>
diff --git a/boards/arm/nucleo_l476rg/nucleo_l476rg.dts b/boards/arm/nucleo_l476rg/nucleo_l476rg.dts
index b096b69..234e8e8 100644
--- a/boards/arm/nucleo_l476rg/nucleo_l476rg.dts
+++ b/boards/arm/nucleo_l476rg/nucleo_l476rg.dts
@@ -24,19 +24,19 @@
 		stop0: state0 {
 			compatible = "zephyr,power-state";
 			power-state-name = "suspend-to-idle";
-			substate-id = <0>;
+			substate-id = <1>;
 			min-residency-us = <500>;
 		};
 		stop1: state1 {
 			compatible = "zephyr,power-state";
 			power-state-name = "suspend-to-idle";
-			substate-id = <1>;
+			substate-id = <2>;
 			min-residency-us = <700>;
 		};
 		stop2: state2 {
 			compatible = "zephyr,power-state";
 			power-state-name = "suspend-to-idle";
-			substate-id = <2>;
+			substate-id = <3>;
 			min-residency-us = <1000>;
 		};
 	};