linux-phytec-fsl

Documentation: net: fsl-fec.txt: Add phy-supply entry

phy-supply is an optional property of the fec driver, so add it to the binding
documentation.

Signed-off-by: Fabio Estevam <fabio.estevam@freescale.com>
Signed-off-by: Rob Herring <rob.herring@calxeda.com>