dt-bindings: mips: Add Luton

Luton SoC belongs to the same family as Ocelot.
Acked-by: Rob Herring <robh@kernel.org>
Signed-off-by: Gregory CLEMENT <gregory.clement@bootlin.com>
Reviewed-by: Alexandre Belloni <alexandre.belloni@bootlin.com>
Signed-off-by: Thomas Bogendoerfer <tsbogend@alpha.franken.de>

Documentation/devicetree/bindings/mips/mscc.txt

@@ -4,7 +4,7 @@ Boards with a SoC of the Microsemi MIPS family shall have the following
 properties:
 
 Required properties:
-- compatible: "mscc,ocelot"
+- compatible: "mscc,ocelot" or "mscc,luton"
 
 
 * Other peripherals: