cxgb4: Add support in cxgb4 to get expansion rom version via ethtool

Add support to get option/expansion rom version flashed in the adapter via
ethtool getdrvinfo function.

Signed-off-by: Hariprasad Shenai <hariprasad@chelsio.com>
Signed-off-by: David S. Miller <davem@davemloft.net>