cpu/x86/smm: Use common SMM_ASEG region

Change-Id: Idca56583c1c8dc41ad11d915ec3e8be781fb4e48
Signed-off-by: Kyösti Mälkki <kyosti.malkki@gmail.com>
Reviewed-on: https://review.coreboot.org/c/coreboot/+/69665
Tested-by: build bot (Jenkins) <no-reply@coreboot.org>
Reviewed-by: Arthur Heymans <arthur@aheymans.xyz>

src/include/cpu/x86/smm.h

@@ -165,6 +165,12 @@ void restore_default_smm_area(void *smm_save_area);
  */
 void smm_region(uintptr_t *start, size_t *size);
 
+static inline void aseg_region(uintptr_t *start, size_t *size)
+{
+	*start = SMM_BASE;
+	*size = SMM_DEFAULT_SIZE; /* SMM_CODE_SEGMENT_SIZE ? */
+}
+
 enum {
 	/* SMM handler area. */
 	SMM_SUBREGION_HANDLER,