dt-bindings: serial: fsl-lpuart: Add imx93 compatible string

The lpuart on i.MX93 is derived from i.MX7ULP with some industrial
enhancements, it uses two compatible strings, so update the
compatible string for i.MX93.
Acked-by: Rob Herring <robh@kernel.org>
Signed-off-by: Peng Fan <peng.fan@nxp.com>
Link: https://lore.kernel.org/r/20220323093659.1722463-1-peng.fan@oss.nxp.comSigned-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

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

@@ -23,7 +23,9 @@ properties:
           - fsl,imx8qxp-lpuart
           - fsl,imxrt1050-lpuart
       - items:
-          - const: fsl,imx8ulp-lpuart
+          - enum:
+              - fsl,imx93-lpuart
+              - fsl,imx8ulp-lpuart
           - const: fsl,imx7ulp-lpuart
       - items:
           - enum: