amd-xgbe: Prepare for supporting PCI devices

Update the driver framework to separate out platform/ACPI specific code
from general code during device initialization. This will allow for the
introduction of PCI device support.

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