ixgbe: Drop probe_vf and merge functionality into ixgbe_enable_sriov

This is meant to fix a bug in which we were not checking for pre-existing
VFs if we were not setting the max_vfs value at driver load.  What happens
now is that we always call ixgbe_enable_sriov and this checks for
pre-existing VFs ore requested VFs prior to deciding on no SR-IOV.

Signed-off-by: Alexander Duyck <alexander.h.duyck@intel.com>
Tested-by: Phil Schmitt <phillip.j.schmitt@intel.com>
Tested-by: Sibai Li <sibai.li@intel.com>
Signed-off-by: Jeff Kirsher <jeffrey.t.kirsher@intel.com>