target-xtensa: implement LSAI group

- base + offset load/store operations for 1/2/4 byte values;
- cache operations (not implemented);
- multiprocessor synchronization operations.

Signed-off-by: Max Filippov <jcmvbkbc@gmail.com>
Signed-off-by: Blue Swirl <blauwirbel@gmail.com>
diff --git a/target-xtensa/cpu.h b/target-xtensa/cpu.h
index f756b43..ac9bbb4 100644
--- a/target-xtensa/cpu.h
+++ b/target-xtensa/cpu.h
@@ -107,6 +107,7 @@
 
 enum {
     SAR = 3,
+    SCOMPARE1 = 12,
 };
 
 typedef struct XtensaConfig {