cxgb4: add cxgb4_fcoe.c for FCoE

This patch adds cxgb4_fcoe.c and enables FCOE_CRC, FCOE_MTU
net device features.

Signed-off-by: Varun Prakash <varun@chelsio.com>
Signed-off-by: David S. Miller <davem@davemloft.net>