ARM: dts: am33xx: Add idle_states for cpuidle

Add idle_states table for CPU on am335x. 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/am33xx.dtsi

@@ -47,6 +47,7 @@ cpus {
 		#size-cells = <0>;
 		cpu@0 {
 			compatible = "arm,cortex-a8";
+			enable-method = "ti,am3352";
 			device_type = "cpu";
 			reg = <0>;
 
@@ -56,6 +57,17 @@ cpu@0 {
 			clock-names = "cpu";
 
 			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 = <90>;
+				min-residency-us = <300>;
+				ti,idle-wkup-m3;
+			};
 		};
 	};