sfc: attach/detach EF100 representors along with their owning PF

Since representors piggy-back on the PF's queues for TX, they can
 only accept new TXes while the PF is up.  Thus, any operation which
 detaches the PF must first detach all its VFreps.

Signed-off-by: Edward Cree <ecree.xilinx@gmail.com>
Signed-off-by: David S. Miller <davem@davemloft.net>