dt: bindings: add ethernet phy eee-broken-modes option documentation

Signed-off-by: Jerome Brunet <jbrunet@baylibre.com>
Reviewed-by: Andreas Färber <afaerber@suse.de>
Signed-off-by: David S. Miller <davem@davemloft.net>

Documentation/devicetree/bindings/net/phy.txt

@@ -38,6 +38,8 @@ Optional Properties:
 - enet-phy-lane-swap: If set, indicates the PHY will swap the TX/RX lanes to
   compensate for the board being designed with the lanes swapped.
 
+- eee-broken-modes: Bits to clear in the MDIO_AN_EEE_ADV register to
+  disable EEE broken modes.
 
 Example: