dt-bindings: net: tja11xx: add nxp,refclk_in property

TJA110x REF_CLK can be configured as interface reference clock
intput or output when the RMII mode enabled. This patch add the
property to make the REF_CLK can be configurable.
Signed-off-by: Wei Fang <wei.fang@nxp.com>
Acked-by: Rob Herring <robh@kernel.org>
Signed-off-by: Jakub Kicinski <kuba@kernel.org>

Documentation/devicetree/bindings/net/nxp,tja11xx.yaml

@@ -31,6 +31,22 @@ patternProperties:
         description:
           The ID number for the child PHY. Should be +1 of parent PHY.
 
+      nxp,rmii-refclk-in:
+        type: boolean
+        description: |
+          The REF_CLK is provided for both transmitted and received data
+          in RMII mode. This clock signal is provided by the PHY and is
+          typically derived from an external 25MHz crystal. Alternatively,
+          a 50MHz clock signal generated by an external oscillator can be
+          connected to pin REF_CLK. A third option is to connect a 25MHz
+          clock to pin CLK_IN_OUT. So, the REF_CLK should be configured
+          as input or output according to the actual circuit connection.
+          If present, indicates that the REF_CLK will be configured as
+          interface reference clock input when RMII mode enabled.
+          If not present, the REF_CLK will be configured as interface
+          reference clock output when RMII mode enabled.
+          Only supported on TJA1100 and TJA1101.
+
     required:
       - reg
 
@@ -44,6 +60,7 @@ examples:
 
         tja1101_phy0: ethernet-phy@4 {
             reg = <0x4>;
+            nxp,rmii-refclk-in;
         };
     };
   - |