arm64: zynqmp: Switch to ethernet-phy-id in kv260

Use ethernet-phy-id compatible string to properly describe phy reset on
kv260 boards. Previous description wasn't correct because reset was done
for mdio bus to operate and it was in this case used for different purpose
which was eth phy reset. With ethernet-phy-id phy reset happens only for
the phy via phy framework.

Signed-off-by: Michal Simek <michal.simek@xilinx.com>
Link: https://lore.kernel.org/r/73b64f1a2b873b4e26bd2b365364bdf313794ae2.1645629459.git.michal.simek@xilinx.com