cxgb4: Add support to recognize 40G links

Also, create a new Common Code interface to translate Firmware Port Technology
Type values (enum fw_port_type) to string descriptions.  This will allow us
to maintain the description translation table in one place rather than in
every driver.

Based on original work by Scott Bardone and Casey Leedom <leedom@chelsio.com>

Signed-off-by: Kumar Sanghvi <kumaras@chelsio.com>
Signed-off-by: David S. Miller <davem@davemloft.net>