eth: lan743x: reject extts for non-pci11x1x devices

Remove PTP_PF_EXTTS support for non-PCI11x1x devices since they do not support
the PTP-IO Input event triggered timestamping mechanisms added

Fixes: 60942c39

 ("net: lan743x: Add support for PTP-IO Event Input External Timestamp (extts)")
Signed-off-by: Raju Lakkaraju <Raju.Lakkaraju@microchip.com>
Reviewed-by: Horatiu Vultur <horatiu.vultur@microchip.com>
Signed-off-by: David S. Miller <davem@davemloft.net>