dt-bindings: net: add support for Microchip KSZ9131

Add support for Microchip Technology KSZ9131 10/100/1000 Ethernet PHY
Signed-off-by: Yuiko Oshino <yuiko.oshino@microchip.com>
Reviewed-by: Rob Herring <robh@kernel.org>
Signed-off-by: David S. Miller <davem@davemloft.net>

Documentation/devicetree/bindings/net/micrel-ksz90x1.txt

-Micrel KSZ9021/KSZ9031 Gigabit Ethernet PHY
+Micrel KSZ9021/KSZ9031/KSZ9131 Gigabit Ethernet PHY
 
 Some boards require special tuning values, particularly when it comes
 to clock delays. You can specify clock delay values in the PHY OF
@@ -64,6 +64,32 @@ KSZ9031:
         Attention: The link partner must be configurable as slave otherwise
         no link will be established.
 
+KSZ9131:
+
+  All skew control options are specified in picoseconds. The increment
+  step is 100ps. Unlike KSZ9031, the values represent picoseccond delays.
+  A negative value can be assigned as rxc-skew-psec = <(-100)>;.
+
+  Optional properties:
+
+    Range of the value -700 to 2400, default value 0:
+
+      - rxc-skew-psec : Skew control of RX clock pad
+      - txc-skew-psec : Skew control of TX clock pad
+
+    Range of the value -700 to 800, default value 0:
+
+      - rxdv-skew-psec : Skew control of RX CTL pad
+      - txen-skew-psec : Skew control of TX CTL pad
+      - rxd0-skew-psec : Skew control of RX data 0 pad
+      - rxd1-skew-psec : Skew control of RX data 1 pad
+      - rxd2-skew-psec : Skew control of RX data 2 pad
+      - rxd3-skew-psec : Skew control of RX data 3 pad
+      - txd0-skew-psec : Skew control of TX data 0 pad
+      - txd1-skew-psec : Skew control of TX data 1 pad
+      - txd2-skew-psec : Skew control of TX data 2 pad
+      - txd3-skew-psec : Skew control of TX data 3 pad
+
 Examples:
 
 	mdio {