net: sparx5: remove phylink_config.pcs_poll usage

Phylink will use PCS polling whenever phylink_config.pcs_poll or the
phylink_pcs poll member is set. As this driver sets both, remove the
former.

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