dt-bindings: net: ethernet-phy: add desciption for ethernet-phy-id1234.d400

The description below is already in use in
'rk3228-evb.dts', 'rk3229-xms6.dts' and 'rk3328.dtsi'
but somehow never added to a document, so add
"ethernet-phy-id1234.d400", "ethernet-phy-ieee802.3-c22"
for ethernet-phy nodes on Rockchip platforms to
'ethernet-phy.yaml'.

Signed-off-by: Johan Jonker <jbx6244@gmail.com>
Acked-by: Florian Fainelli <f.fainelli@gmail.com>
Signed-off-by: David S. Miller <davem@davemloft.net>