arm: dts: am437x: sync cpsw/mdio/phy with latest linux - drop phy_id

Synchronize CPSW/MDIO/PHY DT nodes with latest linux - replace deprecated
phy_id property with phy-handle.

Signed-off-by: Grygorii Strashko <grygorii.strashko@ti.com>
Cc: Lokesh Vutla <lokeshvutla@ti.com>