Documentation: fsl: dspi: Add fsl,ls2080a-dspi compatible string

new compatible string: "fsl,ls2080a-dspi".
Signed-off-by: Yuan Yao <yao.yuan@nxp.com>
Acked-by: Rob Herring <robh@kernel.org>
Signed-off-by: Shawn Guo <shawnguo@kernel.org>

Documentation/devicetree/bindings/spi/spi-fsl-dspi.txt

 ARM Freescale DSPI controller
 
 Required properties:
-- compatible : "fsl,vf610-dspi", "fsl,ls1021a-v1.0-dspi", "fsl,ls2085a-dspi"
+- compatible : "fsl,vf610-dspi", "fsl,ls1021a-v1.0-dspi",
+		"fsl,ls2085a-dspi"
+		or
+		"fsl,ls2080a-dspi" followed by "fsl,ls2085a-dspi"
 - reg : Offset and length of the register set for the device
 - interrupts : Should contain SPI controller interrupt
 - clocks: from common clock binding: handle to dspi clock.