sfc: Remove netdev init from efx_init_struct

Move functionality involving the struct net_device out of
efx_init_struct so that we can initialise without a net dev
for VDPA operation.

Signed-off-by: Jonathan Cooper <jonathan.s.cooper@amd.com>
Co-developed-by: Martin Habets <habetsm.xilinx@gmail.com>
Signed-off-by: Martin Habets <habetsm.xilinx@gmail.com>
Signed-off-by: David S. Miller <davem@davemloft.net>