smm: Clear SMRAM when debugging

This makes it easier to spot unused RAM.

BUG=b:80539294
TEST=built and tested on grunt. Verified unused memory was set to 0xcdcdcdcd

Change-Id: I335eaf642bd8526f31819eaac95ce80c2df3c300
Signed-off-by: Raul E Rangel <rrangel@chromium.org>
Reviewed-on: https://review.coreboot.org/27227
Tested-by: build bot (Jenkins) <no-reply@coreboot.org>
Reviewed-by: Martin Roth <martinroth@google.com>
diff --git a/src/cpu/x86/smm/smm_module_loader.c b/src/cpu/x86/smm/smm_module_loader.c
index 3d7952f..e92fa05 100644
--- a/src/cpu/x86/smm/smm_module_loader.c
+++ b/src/cpu/x86/smm/smm_module_loader.c
@@ -346,6 +346,10 @@
 	if (rmodule_parse(&_binary_smm_start, &smm_mod))
 		return -1;
 
+	/* Clear SMM region */
+	if (IS_ENABLED(CONFIG_DEBUG_SMI))
+		memset(smram, 0xcd, size);
+
 	total_stack_size = params->per_cpu_stack_size *
 			   params->num_concurrent_stacks;