enic: Move the Cisco driver

Move the Cisco driver into drivers/net/ethernet/cisco/ and make the
necessary Kconfig and Makefile changes.

CC: Christian Benvenuti <benve@cisco.com>
CC: Vasanthy Kolluri <vkolluri@cisco.com>
CC: Roopa Prabhu <roprabhu@cisco.com>
CC: David Wang <dwang2@cisco.com>
Signed-off-by: Jeff Kirsher <jeffrey.t.kirsher@intel.com>