net: phy: remove mdio_board_info support from phylib

After having removed mdio_board_info usage from dsa_loop, there's no
user left. So let's drop support for it from phylib.

Signed-off-by: Heiner Kallweit <hkallweit1@gmail.com>
Link: https://patch.msgid.link/01542a2e-05f5-4f13-acef-72632b33b5be@gmail.com


Signed-off-by: Jakub Kicinski <kuba@kernel.org>