net: xilinx: emaclite: add minimal ethtool ops

This set adds a minimal set of ethtool hooks to the driver, which provide a
decent amount of link information via ethtool.
With this change, running `ethtool ethX` in user-space provides all the
neatly-formatted information about the link (what was negotiated, what is
advertised, etc).

Signed-off-by: Alexandru Ardelean <alexandru.ardelean@analog.com>
Reviewed-by: Radhey Shyam Pandey <radhey.shyam.pandey@xilinx.com>
Signed-off-by: David S. Miller <davem@davemloft.net>