dt-bindings: net: cdns,macb: Drop phy-names property for ZynqMP SGMII PHY

In zynqmp SGMII initialization, there is a single PHY so remove phy-names
property as there is no real need of having it.

Signed-off-by: Radhey Shyam Pandey <radhey.shyam.pandey@xilinx.com>
Signed-off-by: David S. Miller <davem@davemloft.net>