ASoC: bindings: fsl-asoc-card: Add compatible string for MQS

Add compatible string "fsl,imx-audio-mqs" for MQS, and move
"audio-routing" property to be optional for MQS doesn't need
such property.

Signed-off-by: Shengjiu Wang <shengjiu.wang@nxp.com>
Link: https://lore.kernel.org/r/2185a3ec866bc59f82d93b73d1a732a896fd8f48.1592369271.git.shengjiu.wang@nxp.com


Signed-off-by: Mark Brown <broonie@kernel.org>