amd-xgbe: Prepare for working with more than one type of phy

Prepare the code to be able to work with more than one type of phy by
adding additional callable functions into the phy interface and removing
phy specific settings/functions from non-phy related files.

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