net: hns: optimize XGE capability by reducing cpu usage

here is the patch raising the performance of XGE by:
1)changes the way page management method for enet momery, and
2)reduces the count of rmb, and
3)adds Memory prefetching

Signed-off-by: Kejian Yan <yankejian@huawei.com>
Signed-off-by: David S. Miller <davem@davemloft.net>