sfc: force removal of VF and vport on driver removal

When the driver unloads, force the unbind and removal of any
VFs in the host with the PF.  The PF cannot remove vports and
vswitches if they are still being used by a VF driver, and when
unloading the sfc driver the removal order is not guaranteed,
so the instruction from the PF to the VF to unbind enforces a
suitable ordering so that vswitches and vports can be removed.

As a result of this, manually unbinding the driver from a single
PF will result in all of its VFs in the host also being removed.

Signed-off-by: Shradha Shah <sshah@solarflare.com>
Signed-off-by: David S. Miller <davem@davemloft.net>