sfc: QT2025C: Work around PHY firmware initialisation bug

The PHY's firmware very occasionally appears to lock up very early, but
with the heartbeat update still running.  Rebooting the microcontroller
core seems to be sufficient to recover.

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