of: documentation: add bindings documentation for TS-4600

This adds the documentation for the TS-4600 by Technologic Systems.
Signed-off-by: Sebastien Bourdelin <sebastien.bourdelin@savoirfairelinux.com>
Acked-by: Rob Herring <robh@kernel.org>
Signed-off-by: Shawn Guo <shawnguo@kernel.org>

Documentation/devicetree/bindings/arm/technologic.txt

 Technologic Systems Platforms Device Tree Bindings
 --------------------------------------------------
 
+TS-4600 is a System-on-Module based on the Freescale i.MX28 System-on-Chip.
+It can be mounted on a carrier board providing additional peripheral connectors.
+Required root node properties:
+	- compatible = "technologic,imx28-ts4600", "fsl,imx28"
+
 TS-4800 board
 Required root node properties:
 	- compatible = "technologic,imx51-ts4800", "fsl,imx51";