env: Rename setenv() to env_set()

We are now using an env_ prefix for environment functions. Rename setenv()
for consistency. Also add function comments in common.h.

Suggested-by: Wolfgang Denk <wd@denx.de>
Signed-off-by: Simon Glass <sjg@chromium.org>
diff --git a/include/search.h b/include/search.h
index 402dfd8..df5d61c 100644
--- a/include/search.h
+++ b/include/search.h
@@ -118,7 +118,7 @@
 #define H_MATCH_SUBSTR	(1 << 7) /* search for substring matches	     */
 #define H_MATCH_REGEX	(1 << 8) /* search for regular expression matches    */
 #define H_MATCH_METHOD	(H_MATCH_IDENT | H_MATCH_SUBSTR | H_MATCH_REGEX)
-#define H_PROGRAMMATIC	(1 << 9) /* indicate that an import is from setenv() */
+#define H_PROGRAMMATIC	(1 << 9) /* indicate that an import is from env_set() */
 #define H_ORIGIN_FLAGS	(H_INTERACTIVE | H_PROGRAMMATIC)
 
 #endif /* _SEARCH_H_ */