sb,soc/intel: Replace smm_southbridge_enable_smi()

Change-Id: I8a2e8b0c104d9e08f07aeb6a2c32106480ace3e5
Signed-off-by: Kyösti Mälkki <kyosti.malkki@gmail.com>
Reviewed-on: https://review.coreboot.org/c/coreboot/+/41961
Tested-by: build bot (Jenkins) <no-reply@coreboot.org>
Reviewed-by: Angel Pons <th3fanbus@gmail.com>

src/include/cpu/intel/smm_reloc.h

@@ -43,7 +43,6 @@ void smm_relocate(void);
  * for clearing the state in the SMM registers. The other is for enabling
  * SMIs. They are split so that other work between the 2 actions. */
 void smm_southbridge_clear_state(void);
-void smm_southbridge_enable_smi(void);
 
 /* To be removed. */
 void smm_initialize(void);