ice: block SF port creation in legacy mode

There is no support for SF in legacy mode. Reflect it in the code.

Reviewed-by: Przemek Kitszel <przemyslaw.kitszel@intel.com>
Fixes: eda69d65 ("ice: add basic devlink subfunctions support")
Signed-off-by: Michal Swiatkowski <michal.swiatkowski@linux.intel.com>
Reviewed-by: Kalesh AP <kalesh-anakkur.purayil@broadcom.com>
Tested-by: Rafal Romanowski <rafal.romanowski@intel.com>
Signed-off-by: Jacob Keller <jacob.e.keller@intel.com>
Reviewed-by: Simon Horman <horms@kernel.org>
Signed-off-by: Paolo Abeni <pabeni@redhat.com>