net: phy: Export mdiobus_register_board_info()

We can build modular code that uses mdiobus_register_board_info() which would
lead to linking failure since this symbol is not expoerted.

Fixes: 648ea01340 ("net: phy: Allow pre-declaration of MDIO devices")
Signed-off-by: Florian Fainelli <f.fainelli@gmail.com>
Reviewed-by: Andrew Lunn <andrew@lunn.ch>
Signed-off-by: David S. Miller <davem@davemloft.net>

drivers/net/phy/mdio-boardinfo.c

@@ -84,3 +84,4 @@ int mdiobus_register_board_info(const struct mdio_board_info *info,
 
 	return 0;
 }
+EXPORT_SYMBOL(mdiobus_register_board_info);