sfc: provide dummy definitions of vswitch functions

sfc: provide dummy definitions of vswitch functions

efx_probe_all() calls efx->type->vswitching_probe during probe. For
SFC4000 (Falcon) NICs this function is not defined, leading to a BUG
with the top of the call stack similar to:
  ? efx_pci_probe_main+0x29a/0x830
  efx_pci_probe+0x7d3/0xe70

vswitching_restore and vswitching_remove also need to be defined.

Fixed in mainline by:
commit 5a6681e22c14 ("sfc: separate out SFC4000 ("Falcon") support into new sfc-falcon driver")

Fixes: 6d8aaaf6f798 ("sfc: create VEB vswitch and vport above default firmware setup")
Signed-off-by: Bert Kenward <bkenward@solarflare.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>