soc/amd: move southbridge_smi_handler to common code

Signed-off-by: Felix Held <felix-coreboot@felixheld.de>
Change-Id: I650498321736eee3d33af51216eda1b650f11744
Reviewed-on: https://review.coreboot.org/c/coreboot/+/50463
Reviewed-by: Marshall Dawson <marshalldawson3rd@gmail.com>
Reviewed-by: Martin Roth <martinroth@google.com>
Tested-by: build bot (Jenkins) <no-reply@coreboot.org>
diff --git a/src/soc/amd/cezanne/smihandler.c b/src/soc/amd/cezanne/smihandler.c
index 2d9e487..b941293 100644
--- a/src/soc/amd/cezanne/smihandler.c
+++ b/src/soc/amd/cezanne/smihandler.c
@@ -1,7 +1,8 @@
 /* SPDX-License-Identifier: GPL-2.0-or-later */
 
-#include <cpu/x86/smm.h>
+#include <amdblocks/smm.h>
 
-void southbridge_smi_handler(void)
+void *get_smi_source_handler(int source)
 {
+	return NULL;
 }