amd-xgbe: Improve SFP 100Mbps auto-negotiation

After changing speed to 100Mbps as a result of auto-negotiation (AN),
some 10/100/1000Mbps SFPs indicate a successful link (no faults or loss
of signal), but cannot successfully transmit or receive data.  These
SFPs required an extra auto-negotiation (AN) after the speed change in
order to operate properly.  Add a quirk for these SFPs so that if the
outcome of the AN actually results in changing to a new speed, re-initiate
AN at that new speed.

Signed-off-by: Tom Lendacky <thomas.lendacky@amd.com>
Signed-off-by: David S. Miller <davem@davemloft.net>