mfd: ti-keystone-devctrl: Add bindings for device state control

The Keystone II devices have a set of registers that are used to control
the status of its peripherals. This node is intended to allow access to
this functionality.

Reviewed-by: Arnd Bergmann <[e-mail]>
Signed-off-by: Ivan Khoronzhuk <[e-mail]>
Signed-off-by: Lee Jones <[e-mail]>

Documentation/devicetree/bindings/mfd/ti-keystone-devctrl.txt

···
+* Device tree bindings for Texas Instruments keystone device state control
+
+The Keystone II devices have a set of registers that are used to control
+the status of its peripherals. This node is intended to allow access to
+this functionality.
+
+Required properties:
+
+- compatible:		"ti,keystone-devctrl", "syscon"
+
+- reg:			contains offset/length value for device state control
+			registers space.
+
+Example:
+
+devctrl: device-state-control@0x02620000 {
+	compatible = "ti,keystone-devctrl", "syscon";
+	reg = <0x02620000 0x1000>;
+};