net: dsa: microchip: ksz9477: separate phylink mode from switch register

As per 'commit 3506b2f4 ("net: dsa: microchip: call
phy_remove_link_mode during probe")' phy_remove_link_mode is added in
the switch_register function after dsa_switch_register. In order to have
the common switch register function, moving this phylink validation to
phylink_get_caps validation hook.

Signed-off-by: Arun Ramadoss <arun.ramadoss@microchip.com>
Signed-off-by: David S. Miller <davem@davemloft.net>