drivers: net: xgene: Add workaround for errata 10GE_1

This patch implements workaround for errata 10GE_1:
10Gb Ethernet port FIFO threshold default values are incorrect.

Signed-off-by: Quan Nguyen <qnguyen@apm.com>
Signed-off-by: Toan Le <toanle@apm.com>
Signed-off-by: Iyappan Subramanian <isubramanian@apm.com>
Tested-by: Fushen Chen <fchen@apm.com>
Signed-off-by: David S. Miller <davem@davemloft.net>