xtensa: reorganize SR referencing

- reference SRs by names where possible, not by numbers;
- get rid of __stringify around SR names where possible;
- remove unneeded SR names from asm/regs.h;
- add SREG_ prefix to remaining SR names;

Signed-off-by: Max Filippov <jcmvbkbc@gmail.com>
Signed-off-by: Chris Zankel <chris@zankel.net>
diff --git a/arch/xtensa/include/asm/cacheflush.h b/arch/xtensa/include/asm/cacheflush.h
index 376cd9d..569fec4 100644
--- a/arch/xtensa/include/asm/cacheflush.h
+++ b/arch/xtensa/include/asm/cacheflush.h
@@ -165,7 +165,7 @@
 static inline u32 xtensa_get_cacheattr(void)
 {
 	u32 r;
-	asm volatile("	rsr %0, CACHEATTR" : "=a"(r));
+	asm volatile("	rsr %0, cacheattr" : "=a"(r));
 	return r;
 }