realtek: mdio: drop SerDes access functionality

realtek: mdio: drop SerDes access functionality

The SerDes access functionality in the mdio-realtek-otto drivers was
meant to be temporary, at least from a certain point on. The user was
all the SerDes configuration that lived in the PHY and DSA drivers.

Now that SerDes configuration has moved completely to the PCS driver,
there is no user of this code anymore. Instead, the PCS driver uses a
separate driver 'mdio-realtek-otto-serdes' to access the SerDes. Thus,
drop all that unused functionality from the "normal" mdio driver.

Signed-off-by: Jonas Jelonek <jelonek.jonas@gmail.com>
Link: https://github.com/openwrt/openwrt/pull/21439
Signed-off-by: Stijn Tintel <stijn@linux-ipv6.be>