dt-bindings: Add new SoCs to bcm4708 DT bindings

Add the 4708, 4709, and 53012 SoCs to the the documentation for the
Broadcom Northstar device tree bindings.
Signed-off-by: Jon Mason <jonmason@broadcom.com>
Acked-by: Hauke Mehrtens <hauke@hauke-m.de>
Acked-by: Scott Branden <sbranden@broadcom.com>
Acked-by: Rob Herring <robh@kernel.org>
Signed-off-by: Florian Fainelli <f.fainelli@gmail.com>

Documentation/devicetree/bindings/arm/bcm/brcm,bcm4708.txt

@@ -5,4 +5,11 @@ Boards with the BCM4708 SoC shall have the following properties:
 
 Required root node property:
 
+bcm4708
 compatible = "brcm,bcm4708";
+
+bcm4709
+compatible = "brcm,bcm4709";
+
+bcm53012
+compatible = "brcm,bcm53012";