arch/x86/include/arch: Add SMM_TASK_STATE_SEG

This define is used to set up the STM SMM Descriptor table tr entry.

Signed-off-by: Eugene D. Myers <edmyers@tycho.nsa.gov>
Change-Id: Iddb1f45444d03465a66a4ebb9fde5f206dc5b300
Reviewed-on: https://review.coreboot.org/c/coreboot/+/38657
Tested-by: build bot (Jenkins) <no-reply@coreboot.org>
Reviewed-by: ron minnich <rminnich@gmail.com>

src/arch/x86/include/arch/rom_segs.h

@@ -18,4 +18,11 @@
 #define ROM_DATA_SEG 0x10
 #define ROM_CODE_SEG64 0x18
 
+/*
+ * This define is placed here to make sure future romstage programmers
+ * know about it.
+ * It is used for STM setup code.
+ */
+#define SMM_TASK_STATE_SEG 0x20
+
 #endif /* ROM_SEGS_H */