ARM: dts: am4372: Add idle_states for cpuidle

Add idle_states table for CPU on am437x. Currently just add C1 state
which gates the MPU clock domain.
Signed-off-by: Dave Gerlach <d-gerlach@ti.com>
Signed-off-by: Tony Lindgren <tony@atomide.com>

arch/arm/boot/dts/am4372.dtsi

@@ -45,6 +45,7 @@ cpus {
 		#size-cells = <0>;
 		cpu: cpu@0 {
 			compatible = "arm,cortex-a9";
+			enable-method = "ti,am4372";
 			device_type = "cpu";
 			reg = <0>;
 
@@ -54,6 +55,17 @@ cpu: cpu@0 {
 			operating-points-v2 = <&cpu0_opp_table>;
 
 			clock-latency = <300000>; /* From omap-cpufreq driver */
+			cpu-idle-states = <&mpu_gate>;
+		};
+
+		idle-states {
+			mpu_gate: mpu_gate {
+				compatible = "arm,idle-state";
+				entry-latency-us = <40>;
+				exit-latency-us = <100>;
+				min-residency-us = <300>;
+				local-timer-stop;
+			};
 		};
 	};