dt-bindings: serial: fsl-lpuart: Add imx8ulp compatible string

The lpuart on i.MX8ULP is derived from i.MX7ULP, it uses two compatible
strings, so update the compatible string for i.MX8ULP.

Reviewed-by: Dong Aisheng <aisheng.dong@nxp.com>
Acked-by: Rob Herring <robh@kernel.org>
Signed-off-by: Jacky Bai <ping.bai@nxp.com>
Signed-off-by: Peng Fan <peng.fan@nxp.com>
Link: https://lore.kernel.org/r/20211120113454.785997-3-peng.fan@oss.nxp.com
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

Documentation/devicetree/bindings/serial/fsl-lpuart.yaml

@@ -22,7 +22,9 @@ properties:
           - fsl,imx7ulp-lpuart
           - fsl,imx8qm-lpuart
       - items:
-          - const: fsl,imx8qxp-lpuart
+          - enum:
+              - fsl,imx8qxp-lpuart
+              - fsl,imx8ulp-lpuart
           - const: fsl,imx7ulp-lpuart
 
   reg: