net: ethernet: fs_enet: drop unused phy_info and mii_if_info

There's no user of the struct phy_info, the 'phy' field and the
mii_if_info in the fs_enet driver, probably dating back when phylib
wasn't as widely used.  Drop these from the driver code.

As the definition for struct mii_if_info is no longer required, drop the
include for linux/mii.h altogether in the driver.

Acked-by: Christophe Leroy <christophe.leroy@csgroup.eu>
Reviewed-by: Christophe Leroy <christophe.leroy@csgroup.eu>
Reviewed-by: Andrew Lunn <andrew@lunn.ch>
Signed-off-by: Maxime Chevallier <maxime.chevallier@bootlin.com>
Signed-off-by: David S. Miller <davem@davemloft.net>