sfc: Add support for QT2025C PHY

This is a new PHY supporting SFP+ modules, used in the SFN4112F
reference design.  It is similar to the QT2022C2 and shares much of
its support code.

Signed-off-by: Ben Hutchings <bhutchings@solarflare.com>
Signed-off-by: David S. Miller <davem@davemloft.net>