enic: Helper code for SRIOV proxy commands

This patch adds helper functions to use PF as proxy for SRIOV VF firmware
commands.

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