iwlwifi: mei: fix linking when tracing is not enabled

I forgot to add stubs in case tracing is disabled which caused linking errors:

ERROR: modpost: "__SCT__tp_func_iwlmei_sap_data" [drivers/net/wireless/intel/iwlwifi/mei/iwlmei.ko] undefined!
ERROR: modpost: "__SCT__tp_func_iwlmei_me_msg" [drivers/net/wireless/intel/iwlwifi/mei/iwlmei.ko] undefined!
ERROR: modpost: "__tracepoint_iwlmei_sap_cmd" [drivers/net/wireless/intel/iwlwifi/mei/iwlmei.ko] undefined!
ERROR: modpost: "__tracepoint_iwlmei_me_msg" [drivers/net/wireless/intel/iwlwifi/mei/iwlmei.ko] undefined!
ERROR: modpost: "__SCK__tp_func_iwlmei_me_msg" [drivers/net/wireless/intel/iwlwifi/mei/iwlmei.ko] undefined!
ERROR: modpost: "__SCK__tp_func_iwlmei_sap_data" [drivers/net/wireless/intel/iwlwifi/mei/iwlmei.ko] undefined!
ERROR: modpost: "__tracepoint_iwlmei_sap_data" [drivers/net/wireless/intel/iwlwifi/mei/iwlmei.ko] undefined!
ERROR: modpost: "__SCT__tp_func_iwlmei_sap_cmd" [drivers/net/wireless/intel/iwlwifi/mei/iwlmei.ko] undefined!
ERROR: modpost: "__SCK__tp_func_iwlmei_sap_cmd" [drivers/net/wireless/intel/iwlwifi/mei/iwlmei.ko] undefined!

Fixes: 2da4366f

 ("iwlwifi: mei: add the driver to allow cooperation with CSME")
Reported-by: Jiri Slaby <jirislaby@kernel.org>
Signed-off-by: Emmanuel Grumbach <emmanuel.grumbach@intel.com>
Acked-by: Luca Coelho <luciano.coelho@intel.com>
Signed-off-by: Kalle Valo <kvalo@kernel.org>
Link: https://lore.kernel.org/r/20211201113411.130409-1-emmanuel.grumbach@intel.com