of: of_mdio: Add a whitelist of PHY compatibilities.

Some phy nodes list a compatible value indicating the PHY make/model.
This is never used to match the device to the driver. However it does
confuse the code to separate a PHY from a generic MDIO device like a
switch. Generic MDIO devices must have a compatible value, PHYs can
list clause 22 or 45, but nothing else.

Issue a warning if we find a compatible value known on the whitelist,
and say it is a PHY.

Fixes: a9049e0c

 ("mdio: Add support for mdio drivers.")
Reported-by: Aaro Koskinen <aaro.koskinen@nokia.com>
Reported-by: Olof Johansson <olof@lixom.net>
Tested-by: Aaro Koskinen <aaro.koskinen@nokia.com>
Signed-off-by: Andrew Lunn <andrew@lunn.ch>
Signed-off-by: David S. Miller <davem@davemloft.net>