drivers: net: xgene: Fix the ACPI support for RGMII/SGMII0/XFI interface of APM X-Gene SoC ethernet controller.

This patch implements couple of fixes to support ACPI for RGMII/SGMII0/XFI
interface of APM X-Gene SoC ethernet controller driver. This patch uses
the _SUN acpi object to fetch the port-id information whereas the FDT uses
port-id binding for port-id information.
Signed-off-by: Iyappan Subramanian <isubramanian@apm.com>
Signed-off-by: Suman Tripathi <stripathi@apm.com>
Signed-off-by: David S. Miller <davem@davemloft.net>