ARM: zynq: DT: Fix Ethernet phy modes

The used PHYs should be qualified as 'rgmii-id' instead of just 'rgmii'.
For the Zed board this seems to make a difference between working and
broken Ethernet.

Signed-off-by: Soren Brinkmann <soren.brinkmann@xilinx.com>
Signed-off-by: Michal Simek <michal.simek@xilinx.com>