i40e: Move code to enable/disable Loopback to the main file

i40e: Move code to enable/disable Loopback to the main file

Since changes made to enable or disable loopback for all VSIs, not only SR-IOV
or PCIOV, then it became necessary to move the associated functions to main
file - so that other non-SRIOV supported driver can take advantage of the
changes.

Change-ID: I59a49fd23a6136acda5e16f8d1e5ac7fd9c5fc05
Signed-off-by: Akeem G Abodunrin <akeem.g.abodunrin@intel.com>
Signed-off-by: Jesse Brandeburg <jesse.brandeburg@intel.com>
Signed-off-by: Jeff Kirsher <jeffrey.t.kirsher@intel.com>