dt-bindings: dsp: fsl: Add SOF compatile string for i.MX8ULP

Add SOF compatile string "fsl,imx8ulp-dsp" for supporting DSP
device on i.MX8ULP platform.

Signed-off-by: Shengjiu Wang <shengjiu.wang@nxp.com>
Acked-by: Rob Herring <robh@kernel.org>
Reviewed-by: Daniel Baluta <daniel.baluta@nxp.com>
Link: https://lore.kernel.org/r/1660787634-28550-1-git-send-email-shengjiu.wang@nxp.com


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