amd-xgbe-phy: Check device for current speed mode (KR/KX)

Since device resets can change the current mode it's possible to think
the device is in a different mode than it actually is.  Rather than
trying to determine every place that is needed to set/save the current
mode, be safe and check the devices actual mode when needed rather than
trying to track it.

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