ixgbe: Reconfigure SR-IOV Init

Use the PCI device flag indicating if a VF is assigned to a guest VM
to guard against destroying VFs upon driver removal.  Implement
additional feature to detect if VFs already exist when the driver
is loaded and if so configure them and set the driver state to
SR-IOV enabled.

Signed-off-by: Greg Rose <gregory.v.rose@intel.com>
Signed-off-by: Jeff Kirsher <jeffrey.t.kirsher@intel.com>