dt-bindings: net: phy: smsc: document reference clock

Add support to specify the reference clock for the phy.

Signed-off-by: Marco Felsch <[e-mail]>
Reviewed-by: Florian Fainelli <[e-mail]>
Signed-off-by: David S. Miller <[e-mail]>

Documentation/devicetree/bindings/net/smsc-lan87xx.txt

···
 
 Optional properties:
 
+- clocks:
+  The clock used as phy reference clock and is connected to phy
+  pin XTAL1/CLKIN.
+
 - smsc,disable-energy-detect:
   If set, do not enable energy detect mode for the SMSC phy.
   default: enable energy detect mode