net: ks8851: Select PHYLIB and MICREL_PHY in Kconfig

The PHYLIB must be selected to provide mdiobus_*() functions, and the
MICREL_PHY is necessary too, as that is the only possible PHY attached
to the KS8851 (it is the internal PHY).

Fixes: ef363122 ("net: ks8851: Register MDIO bus and the internal PHY")
Signed-off-by: Marek Vasut <marex@denx.de>
Cc: Heiner Kallweit <hkallweit1@gmail.com>
Cc: Lukas Wunner <lukas@wunner.de>
Reviewed-by: Andrew Lunn <andrew@lunn.ch>
Link: https://lore.kernel.org/r/20210111125046.36326-1-marex@denx.de


Signed-off-by: Jakub Kicinski <kuba@kernel.org>