dt-bindings: imx6q-pcie: Add iMX8MM PCIe compatible string

Add the i.MX8MM PCIe compatible string.
Signed-off-by: NRichard Zhu <hongxing.zhu@nxp.com>
Reviewed-by: NLucas Stach <l.stach@pengutronix.de>
Signed-off-by: NRob Herring <robh@kernel.org>
Link: https://lore.kernel.org/r/1646293805-18248-1-git-send-email-hongxing.zhu@nxp.com

Documentation/devicetree/bindings/pci/fsl,imx6q-pcie.yaml

@@ -25,6 +25,7 @@ properties:
       - fsl,imx6qp-pcie
       - fsl,imx7d-pcie
       - fsl,imx8mq-pcie
+      - fsl,imx8mm-pcie
 
   reg:
     items: