net: sfp: add quirk for FS's 2.5G copper SFP

Add a quirk for a copper SFP that identifies itself as "FS" "SFP-2.5G-T".
This module's PHY is inaccessible, and can only run at 2500base-X with the
host without negotiation. Add a quirk to enable the 2500base-X interface mode
with 2500base-T support and disable auto negotiation.

Signed-off-by: Raju Lakkaraju <Raju.Lakkaraju@microchip.com>
Link: https://lore.kernel.org/r/20230925080059.266240-1-Raju.Lakkaraju@microchip.com
Signed-off-by: Paolo Abeni <pabeni@redhat.com>