Import patch "net: phy: realtek: mark existing MMDs as present"

    When using Clause-45 mode to access RealTek RTL8221B 2.5G PHYs some
    versions of the PHY fail to report the MMDs present on the PHY.
    Mark MMDs PMAPMD, PCS and AN which are always existing according to
    the datasheet as present to fix that.

Fixes: #16823, #17183, #17232
Signed-off-by: Daniel Golle <daniel@makrotopia.org>
Tested-by: Aleksander Jan Bajkowski <olek2@wp.pl>
Tested-by: Juan Pedro Paredes Caballero <juanpedro.paredes@gmail.com>