cxgb4: change the port capability bits definition

MDI Port Capabilities bit definitions were inconsistent with
regard to the MDI enum values. 2 bits used to define MDI in
the port capabilities are not really separable, it's a 2-bit
field with 4 different values. Change the port capability bit
definitions to be "AUTO" and "STRAIGHT" in order to get them
to line up with the enum's.

Signed-off-by: Casey Leedom <leedom@chelsio.com>
Signed-off-by: Ganesh Goudar <ganeshgr@chelsio.com>
Signed-off-by: David S. Miller <davem@davemloft.net>