net: dwc_eth_qos: Fold board_interface_eth_init into STM32 glue code

net: dwc_eth_qos: Fold board_interface_eth_init into STM32 glue code

Move board_interface_eth_init() into eqos_probe_syscfg_stm32() in STM32
driver glue code. The eqos_probe_syscfg_stm32() parses STM32 specific DT
properties of this MAC and configures SYSCFG registers accordingly, there
is nothing board specific happening in this function, move it into generic
driver code instead. Drop the now unused duplicates from board files.

Reviewed-by: Patrice Chotard <patrice.chotard@foss.st.com>
Signed-off-by: Marek Vasut <marex@denx.de>