octeon_ep: add ethtool support for Octeon PCI Endpoint NIC

Add support for the following ethtool commands:

ethtool -i|--driver devname
ethtool devname
ethtool -s devname [speed N] [autoneg on|off] [advertise N]
ethtool -S|--statistics devname

Signed-off-by: Veerasenareddy Burru <vburru@marvell.com>
Signed-off-by: Abhijit Ayarekar <aayarekar@marvell.com>
Signed-off-by: Satananda Burla <sburla@marvell.com>
Signed-off-by: David S. Miller <davem@davemloft.net>