amd-xgbe: Always attempt link training in KR mode

Link training is always attempted when in KR mode, but the code is
structured to check if link training has been enabled before attempting
to perform it.  Since that check will always be true, simplify the code
to always enable and start link training during KR auto-negotiation.

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