net: dsa: microchip: prepare PHY for proper advertisement

Prepare PHY for proper advertisement as sometimes the PHY in the switch
has its own problems even though it may share the PHY id from regular PHY
but the fixes in the PHY driver do not apply.

Signed-off-by: Tristram Ha <Tristram.Ha@microchip.com>
Reviewed-by: Andrew Lunn <andrew@lunn.ch>
Reviewed-by: Florian Fainelli <f.fainelli@gmail.com>
Signed-off-by: David S. Miller <davem@davemloft.net>