arm64: dts: imx8ulp: add cpuidle node

Add cpuidle node and enable cpuidle for dual cores. The HW mode in
Arm Trusted Firmware is SoC Application Power Domain Sleep mode.

Signed-off-by: Jacky Bai <ping.bai@nxp.com>
Signed-off-by: Peng Fan <peng.fan@nxp.com>
Signed-off-by: Shawn Guo <shawnguo@kernel.org>

arch/arm64/boot/dts/freescale/imx8ulp.dtsi

@@ -40,6 +40,7 @@
 			reg = <0x0 0x0>;
 			enable-method = "psci";
 			next-level-cache = <&A35_L2>;
+			cpu-idle-states = <&cpu_sleep>;
 		};
 
 		A35_1: cpu@1 {
@@ -48,6 +49,7 @@
 			reg = <0x0 0x1>;
 			enable-method = "psci";
 			next-level-cache = <&A35_L2>;
+			cpu-idle-states = <&cpu_sleep>;
 		};
 
 		A35_L2: l2-cache0 {
@@ -55,6 +57,19 @@
 			cache-level = <2>;
 			cache-unified;
 		};
+
+		idle-states {
+			entry-method = "psci";
+
+			cpu_sleep: cpu-sleep {
+				compatible = "arm,idle-state";
+				arm,psci-suspend-param = <0x0>;
+				local-timer-stop;
+				entry-latency-us = <1000>;
+				exit-latency-us = <700>;
+				min-residency-us = <2700>;
+			};
+		};
 	};
 
 	gic: interrupt-controller@2d400000 {