sfc: do not try to call tc functions when CONFIG_SFC_SRIOV=n

Functions efx_tc_netdev_event and efx_tc_netevent_event do not exist
 in that case as object files tc_bindings.o and tc_encap_actions.o
 are not built, so the calls to them from ef100_netdev_event and
 ef100_netevent_event cause link errors.
Wrap the corresponding header files (tc_bindings.h, tc_encap_actions.h)
 with #if IS_ENABLED(CONFIG_SFC_SRIOV), and add an #else with static
 inline stubs for these two functions.

Reported-by: kernel test robot <lkp@intel.com>
Closes: https://lore.kernel.org/oe-kbuild-all/202306102026.ISK5JfUQ-lkp@intel.com/
Fixes: 7e5e7d80

 ("sfc: neighbour lookup for TC encap action offload")
Signed-off-by: Edward Cree <ecree.xilinx@gmail.com>
Reviewed-by: Martin Habets <habetsm.xilinx@gmail.com>
Signed-off-by: David S. Miller <davem@davemloft.net>