Merge branch 'remove-kconfig-sysmbol-mdio_bus'

Heiner Kallweit says:

====================
remove Kconfig sysmbol MDIO_BUS

MDIO-based regmap is the last user of config symbol MDIO_BUS.
MDIO access needs a MII bus, which requires PHYLIB for the provider part.
Therefore make REGMAP_MDIO depend on PHYLIB, what allows to remove
config symbol MDIO_BUS.
====================

Link: https://patch.msgid.link/bc63cf87-3dba-4ab6-9c84-caa7357c3273@gmail.com
Signed-off-by: Jakub Kicinski <kuba@kernel.org>