ARCH_MAX board uses 0x01 as PHY address, different from other NUCLEO STM32 boards. To faciliate change of PHY address of customized boards, a configuration entry eth-phyaddr was added and can be overriden as needed in mbed_app.json by adding "stm32-emac.eth-phyaddr": X. Macro ETH_ARCH_PHY_ADDRESS was also renamed to ETH_PHY_ADDRESS, because it is not only used by ARCH_MAX board but also other boards.