dt-bindings: mailbox: imx-mu: add i.MX93 MU

Add bindings for i.MX93 MU which derived from i.MX8ULP
Reviewed-by: Krzysztof Kozlowski <krzysztof.kozlowski@canonical.com>
Acked-by: Rob Herring <robh@kernel.org>
Signed-off-by: Peng Fan <peng.fan@nxp.com>
Signed-off-by: Jassi Brar <jaswinder.singh@linaro.org>

Documentation/devicetree/bindings/mailbox/fsl,mu.yaml

@@ -30,6 +30,9 @@ properties:
       - const: fsl,imx8-mu-scu
       - const: fsl,imx8-mu-seco
       - const: fsl,imx8ulp-mu-s4
+      - items:
+          - const: fsl,imx93-mu
+          - const: fsl,imx8ulp-mu
       - items:
           - enum:
               - fsl,imx7s-mu