spi: dt-bindings: fsl-dspi: add compatible string 'fsl,lx2160a-dspi'

Add compatible string 'fsl,lx2160a-dspi' and allow fall back to
'fsl,ls2085a-dspi'.
Fix below CHECK_DTBS warning.

arch/arm64/boot/dts/freescale/fsl-lx2160a-bluebox3.dtb: spi@2100000: compatible: 'oneOf' conditional failed, one must be fixed:
        ['fsl,lx2160a-dspi', 'fsl,ls2085a-dspi'] is too long

Signed-off-by: Frank Li <Frank.Li@nxp.com>
Link: https://patch.msgid.link/20240703165931.2325807-2-Frank.Li@nxp.com
Signed-off-by: Mark Brown <broonie@kernel.org>