mfd: AS3722: Add dt node properties for system power controller

ams AS3722 device supports the power off by turning off its all rails.

Add dt node properties to enable this functionality on this device.
Signed-off-by: Laxman Dewangan <ldewangan@nvidia.com>
Tested-by: Stephen Warren <swarren@nvidia.com>
Signed-off-by: Anton Vorontsov <anton@enomsg.org>

Documentation/devicetree/bindings/mfd/as3722.txt

@@ -112,6 +112,15 @@ Following are properties of regulator subnode.
 		ams,enable-tracking: Enable tracking with SD1, only supported
 			by LDO3.
 
+Power-off:
+=========
+AS3722 supports the system power off by turning off all its rail. This
+is provided through pm_power_off.
+The device node should have the following properties to enable this
+functionality
+ams,system-power-controller: Boolean, to enable the power off functionality
+        through this device.
+
 Example:
 --------
 #include <dt-bindings/mfd/as3722.h>
@@ -120,6 +129,8 @@ ams3722 {
 	compatible = "ams,as3722";
 	reg = <0x48>;
 
+	ams,system-power-controller;
+
 	interrupt-parent = <&intc>;
 	interrupt-controller;
 	#interrupt-cells = <2>;