enic: Clean up: Organize devcmd wrapper routines

Organize the wrapper routines for firmware devcmds into a separate file.

Signed-off-by: Christian Benvenuti <benve@cisco.com>
Signed-off-by: Vasanthy Kolluri <vkolluri@cisco.com>
Signed-off-by: Roopa Prabhu <roprabhu@cisco.com>
Signed-off-by: David Wang <dwang2@cisco.com>
Signed-off-by: David S. Miller <davem@davemloft.net>