net: mvpp2: clean up mvpp2_phylink_validate()

mvpp2_phylink_validate() no longer needs to check for
PHY_INTERFACE_MODE_NA as phylink will walk the supported interface
types to discover the link mode capabilities. Remove these checks.

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