ASoC: fsl_esai: Add new compatible string for imx6ull

Add new compatible string "fsl,imx6ull-esai" in the binding document.

Signed-off-by: Shengjiu Wang <shengjiu.wang@nxp.com>
Acked-by: Nicolin Chen <nicoleotsuka@gmail.com>
Link: https://lore.kernel.org/r/1565346467-5769-2-git-send-email-shengjiu.wang@nxp.com


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