amd-xgbe: Improve KR auto-negotiation and training

Update xgbe-phy-v2.c to make use of the auto-negotiation (AN) phy hooks
to improve the ability to successfully complete Clause 73 AN when running
at 10gbps.  Hardware can sometimes have issues with CDR lock when the
AN DME page exchange is being performed.

The AN and KR training hooks are used as follows:
- The pre AN hook is used to disable CDR tracking in the PHY so that the
  DME page exchange can be successfully and consistently completed.
- The post KR training hook is used to re-enable the CDR tracking so that
  KR training can successfully complete.
- The post AN hook is used to check for an unsuccessful AN which will
  increase a CDR tracking enablement delay (up to a maximum value).

Add two debugfs entries to allow control over use of the CDR tracking
workaround.  The debugfs entries allow the CDR tracking workaround to
be disabled and determine whether to re-enable CDR tracking before or
after link training has been initiated.

Also, with these changes the receiver reset cycle that is performed during
the link status check can be performed less often.

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