sfc/siena: Reinstate SRIOV init/fini function calls

They were removed in the first series since they were not used for EF10.
Put that code back for Siena, with the prototypes in siena_sriov.h
since that file is a more applicable place for it.

Reported-by: kernel test robot <lkp@intel.com>
Signed-off-by: Martin Habets <habetsm.xilinx@gmail.com>
Signed-off-by: Jakub Kicinski <kuba@kernel.org>