xtensa: rename MISC SR definition to avoid name clashes

There are other special register that cause build warnings and may as
well need renaming as well.
Signed-off-by: NMax Filippov <jcmvbkbc@gmail.com>
Signed-off-by: NChris Zankel <chris@zankel.net>

arch/xtensa/include/asm/regs.h

@@ -66,7 +66,7 @@
 #define ICOUNTLEVEL	237
 #define EXCVADDR	238
 #define CCOMPARE	240
-#define MISC		244
+#define MISC_SR		244
 
 /*  Special names for read-only and write-only interrupt registers.  */