dt-bindings: net: mtk-star-emac: add description for new properties

Add description for new properties which will be parsed in driver.
Signed-off-by: Biao Huang <biao.huang@mediatek.com>
Acked-by: Rob Herring <robh@kernel.org>
Signed-off-by: David S. Miller <davem@davemloft.net>

Documentation/devicetree/bindings/net/mediatek,star-emac.yaml

@@ -48,6 +48,22 @@ properties:
       Phandle to the device containing the PERICFG register range. This is used
       to control the MII mode.
 
+  mediatek,rmii-rxc:
+    type: boolean
+    description:
+      If present, indicates that the RMII reference clock, which is from external
+      PHYs, is connected to RXC pin. Otherwise, is connected to TXC pin.
+
+  mediatek,rxc-inverse:
+    type: boolean
+    description:
+      If present, indicates that clock on RXC pad will be inversed.
+
+  mediatek,txc-inverse:
+    type: boolean
+    description:
+      If present, indicates that clock on TXC pad will be inversed.
+
   mdio:
     $ref: mdio.yaml#
     unevaluatedProperties: false