amd-xgbe-phy: Enhance parallel detection to support KR speed

Add support to allow parallel detection to work in KR speed. With
both speed modes of KX and KR supported, KX must be checked first.

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