dt-bindings: fsl,layerscape-dcfg: add missing compatible for lx2160a

The compatible string is already in use, fix the chip list in binding to
include it.
Signed-off-by: Li Yang <leoyang.li@nxp.com>
Acked-by: Rob Herring <robh@kernel.org>

Documentation/devicetree/bindings/arm/freescale/fsl,layerscape-dcfg.txt

@@ -8,7 +8,7 @@ Required properties:
   - compatible: Should contain a chip-specific compatible string,
 	Chip-specific strings are of the form "fsl,<chip>-dcfg",
 	The following <chip>s are known to be supported:
-	ls1012a, ls1021a, ls1043a, ls1046a, ls2080a.
+	ls1012a, ls1021a, ls1043a, ls1046a, ls2080a, lx2160a
 
   - reg : should contain base address and length of DCFG memory-mapped registers