fjes: Enhance ethtool -S for fjes driver

This patch enhances ethtool -S for fjes driver so that
EP related statistics can be retrieved.

The following statistics can be displayed via ethtool -S:

     ep%d_com_regist_buf_exec
     ep%d_com_unregist_buf_exec
     ep%d_send_intr_rx
     ep%d_send_intr_unshare
     ep%d_send_intr_zoneupdate
     ep%d_recv_intr_rx
     ep%d_recv_intr_unshare
     ep%d_recv_intr_stop
     ep%d_recv_intr_zoneupdate
     ep%d_tx_buffer_full
     ep%d_tx_dropped_not_shared
     ep%d_tx_dropped_ver_mismatch
     ep%d_tx_dropped_buf_size_mismatch
     ep%d_tx_dropped_vlanid_mismatch

Signed-off-by: Taku Izumi <izumi.taku@jp.fujitsu.com>
Signed-off-by: David S. Miller <davem@davemloft.net>