dt-binding: mrvl-gpio: remove orion-gpio description

The Orion GPIO controller binding description in mrvl-gpio.txt is obsolete, and
duplicates the description in gpio-mvebu.txt.
Signed-off-by: Baruch Siach <baruch@tkos.co.il>
Reviewed-by: Andrew Lunn <andrew@lunn.ch>
Signed-off-by: Gregory CLEMENT <gregory.clement@free-electrons.com>

Documentation/devicetree/bindings/gpio/mrvl-gpio.txt

@@ -44,26 +44,3 @@ Example for a PXA3xx platform:
 		interrupt-controller;
 		#interrupt-cells = <0x2>;
 	};
-
-* Marvell Orion GPIO Controller
-
-Required properties:
-- compatible         : Should be "marvell,orion-gpio"
-- reg                : Address and length of the register set for controller.
-- gpio-controller    : So we know this is a gpio controller.
-- ngpio              : How many gpios this controller has.
-- interrupts	     : Up to 4 Interrupts for the controller.
-
-Optional properties:
-- mask-offset        : For SMP Orions, offset for Nth CPU
-
-Example:
-
-		gpio0: gpio@10100 {
-			compatible = "marvell,orion-gpio";
-			#gpio-cells = <2>;
-			gpio-controller;
-			reg = <0x10100 0x40>;
-			ngpio = <32>;
-			interrupts = <35>, <36>, <37>, <38>;
-		};