dt-bindings: imx6q-pcie: Add "pcie_aux" clock for imx8mq

Add a binding for an extra clock required on i.MX8MQ.

Signed-off-by: Andrey Smirnov <[e-mail]>
Signed-off-by: Lorenzo Pieralisi <[e-mail]>
Reviewed-by: Lucas Stach <[e-mail]>
Cc: Bjorn Helgaas <[e-mail]>
Cc: Fabio Estevam <[e-mail]>
Cc: Chris Healy <[e-mail]>
Cc: Lucas Stach <[e-mail]>
Cc: Leonard Crestez <[e-mail]>
Cc: "A.s. Dong" <[e-mail]>
Cc: Richard Zhu <[e-mail]>
Cc: [e-mail]
Cc: [e-mail]
Cc: [e-mail]
Cc: [e-mail]
Cc: Rob Herring <[e-mail]>
Cc: [e-mail]

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

···
 	       - "turnoff"
 - fsl,imx7d-pcie-phy: A phandle to an fsl,imx7d-pcie-phy node.
 
+Additional required properties for imx8mq-pcie:
+- clock-names: Must include the following additional entries:
+	- "pcie_aux"
+
 Example:
 
 	pcie@01000000 {