net: phy: qcom: qca808x: fill in possible_interfaces

Currently QCA808x driver does not fill the possible_interfaces.
2.5G QCA808x support SGMII and 2500Base-X while 1G model only supports
SGMII, so fill the possible_interfaces accordingly.

Signed-off-by: Robert Marko <robimarko@gmail.com>
Reviewed-by: Russell King (Oracle) <rmk+kernel@armlinux.org.uk>
Signed-off-by: David S. Miller <davem@davemloft.net>