amd-xgbe: Use proper DT / ACPI precedence checking

Device tree presence takes precedence over ACPI in the device_* APIs.
The amd-xgbe driver should follow the same precedence. Update the check
on whether to use DT / ACPI to follow this.

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