drivers: ethernet: eth_stm32_hal: Configurable speed and duplex

Make it possible to be able to change speed and duplex for the
STM32H7xx and API_V2 from the configuration settings.

This exists for the non-STM32H7x already today, so this is basically
copying the code for the other STM32's.

Please note that ST has a series incompability. For F1 and F2,
the duplex settings are named ETH_MODE_FULLDUPLEX respective
ETH_MODE_HALFDUPLEX. For F4, H7 and F7 the duplex settings are named
ETH_FULLDUPLEX_MODE respective ETG_HALFDUPLEX_MODE.

This should really be queried from the PHY (as previous programmer have
written in the code). But while waiting for a proper PHY solution,
this is intended as a stop-gap solution.

Signed-off-by: Stefan Petersen <spe@ciellt.se>