dt-bindings: net: ethernet-controller: add PSGMII mode

Add a new PSGMII mode which is similar to QSGMII with the difference being
that it combines 5 SGMII lines into a single link compared to 4 on QSGMII.

It is commonly used by Qualcomm on their QCA807x PHY series.

Signed-off-by: Robert Marko <[e-mail]>
Acked-by: Rob Herring <[e-mail]>
Signed-off-by: David S. Miller <[e-mail]>

Documentation/devicetree/bindings/net/ethernet-controller.yaml

···
       - mii
       - gmii
       - sgmii
+      - psgmii
       - qsgmii
       - qusgmii
       - tbi