sfc: QT2025C: Switch into self-configure mode when not in loopback

The PHY boots in a mode which is not necessarily optimal.  This change
switches it to self-configure mode (except when in loopback, which
won't work in that mode if an SFP+ module is not present) by rebooting
the PHY's microcontroller, and replicating the sequence of configuration
writes from the boot EEPROM with the appropriate changes.

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