i40e: Refactor and cleanup i40e_open(), adding i40e_vsi_open()

This patch cleans up and moves a portion of i40e_open to i40e_vsi_open,
in order to have a shorter vsi_open function that does only that.

Change-ID: I1c418dda94dcfc0eb7d4386a70c330692ef5ecc9
Signed-off-by: Elizabeth Kappler <elizabeth.m.kappler@intel.com>
Signed-off-by: Akeem G Abodunrin <akeem.g.abodunrin@intel.com>
Signed-off-by: Catherine Sullivan <catherine.sullivan@intel.com>
Tested-by: Kavindya Deegala <kavindya.s.deegala@intel.com>
Signed-off-by: Jeff Kirsher <jeffrey.t.kirsher@intel.com>