drivers: net: xgene: Workaround for HW errata 10GE_10/ENET_15

This patch adds workaround for HW errata 10GE_10 and ENET_15:
"HW statistic counters value are duplicated".

- RFCS duplicates RALN counter
- RFLR duplicates RUND counter
- TFCS duplicates TFRG counter
- RALN should be intepreted as 0 in 10G mode

Signed-off-by: Quan Nguyen <qnguyen@apm.com>
Signed-off-by: Iyappan Subramanian <isubramanian@apm.com>
Signed-off-by: David S. Miller <davem@davemloft.net>