drivers: ethernet: eth_stm32_hal: support `get_phy`

[clamattia]

Is your enhancement proposal related to a problem? Please describe.
It is not possible to access the lower layers to get information about them currently. For example link-speed.

Describe the solution you'd like
The driver implements get_phy.

Describe alternatives you've considered
There is other ways to access this information, but I could not find any. Maybe it could be done with get_config (see #84898 ).

Additional context
None