pinctrl: cygnus: Optional DT property to support pin mappings

If GPIO controller's pins are muxed, pin-controller subsystem
need to be intimated by defining mapping between gpio and
pinmux controller. This patch adds required properties to
define this mapping via DT.
Signed-off-by: Pramod Kumar <pramodku@broadcom.com>
Reviewed-by: Ray Jui <rjui@broadcom.com>
Reviewed-by: Scott Branden <sbranden@broadcom.com>
Acked-by: Rob Herring <robh@kernel.org>
Signed-off-by: Linus Walleij <linus.walleij@linaro.org>

Documentation/devicetree/bindings/pinctrl/brcm,cygnus-gpio.txt

@@ -26,9 +26,13 @@ Optional properties:
 - interrupt-controller:
     Specifies that the node is an interrupt controller
 
-- pinmux:
-    Specifies the phandle to the IOMUX device, where pins can be individually
-muxed to GPIO
+- gpio-ranges:
+    Specifies the mapping between gpio controller and pin-controllers pins.
+    This requires 4 fields in cells defined as -
+    1. Phandle of pin-controller.
+    2. GPIO base pin offset.
+    3  Pin-control base pin offset.
+    4. number of gpio pins which are linearly mapped from pin base.
 
 Supported generic PINCONF properties in child nodes:
 
@@ -78,6 +82,8 @@ Example:
 		gpio-controller;
 		interrupts = <GIC_SPI 174 IRQ_TYPE_LEVEL_HIGH>;
 		interrupt-controller;
+		gpio-ranges = <&pinctrl 0 42 1>,
+				<&pinctrl 1 44 3>;
 	};
 
 	/*