net: ena: Use pci_sriov_configure_simple() to enable VFs

Instead of implementing our own version of a SR-IOV configuration stub in
the ena driver, use the existing pci_sriov_configure_simple() function.

Signed-off-by: Alexander Duyck <alexander.h.duyck@intel.com>
Signed-off-by: Bjorn Helgaas <bhelgaas@google.com>
Reviewed-by: Greg Rose <gvrose8192@gmail.com>
Reviewed-by: Christoph Hellwig <hch@lst.de>