net: sxgbe: add EEE(Energy Efficient Ethernet) for Samsung sxgbe

Added support for the EEE(Energy Efficient Ethernet) in 10G ethernet driver.

Signed-off-by: Girish K S <ks.giri@samsung.com>
Neatening-by: Joe Perches <joe@perches.com>
Signed-off-by: Byungho An <bh74.an@samsung.com>
Signed-off-by: David S. Miller <davem@davemloft.net>