sfc: add EF100 VF support via a write to sriov_numvfs

This patch extends the EF100 PF driver by adding .sriov_configure()
which would allow users to enable and disable virtual functions
using the sriov sysfs.

Signed-off-by: Pieter Jansen van Vuuren <pieter.jansen-van-vuuren@amd.com>
Signed-off-by: Edward Cree <ecree.xilinx@gmail.com>
Link: https://lore.kernel.org/r/75e74d9e-14ce-0524-9668-5ab735a7cf62@gmail.com


Signed-off-by: Jakub Kicinski <kuba@kernel.org>