net: phy: realtek: add missing page operations

Add missing page operation callbacks to few Realtek drivers.
This also fixes a NPE after the referenced commit added code to the
RTL8211E driver that uses phy_select_page().

Fixes: f81dadbc ("net: phy: realtek: Add rtl8211e rx/tx delays config")
Signed-off-by: Heiner Kallweit <hkallweit1@gmail.com>
Reviewed-by: Florian Fainelli <f.fainelli@gmail.com>
Reported-by: Vicente Bergas <vicencb@gmail.com>
Signed-off-by: David S. Miller <davem@davemloft.net>