sfc: Wait for MC reboot to complete before scheduling driver reset

Scheduling a reset following an MC reboot event before waiting for
reboot to complete results in a race that can lead to a state where
must_realloc_vis is false in efx_ef10_fini_dmaq() but the VIs have
been destroyed during the MC reboot.

To avoid MC errors when trying to remove VIs that do not exist, wait
for the MC reboot to complete before scheduling the reset.

Signed-off-by: Ben Hutchings <bhutchings@solarflare.com>