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/board/wandboard/wandboard.c b/board/wandboard/wandboard.c
index 1dbc966..adfcf48 100644
--- a/board/wandboard/wandboard.c
+++ b/board/wandboard/wandboard.c
@@ -425,14 +425,14 @@
 
 #ifdef CONFIG_ENV_VARS_UBOOT_RUNTIME_CONFIG
 	if (is_mx6dq())
-		setenv("board_rev", "MX6Q");
+		env_set("board_rev", "MX6Q");
 	else
-		setenv("board_rev", "MX6DL");
+		env_set("board_rev", "MX6DL");
 
 	if (is_revc1())
-		setenv("board_name", "C1");
+		env_set("board_name", "C1");
 	else
-		setenv("board_name", "B1");
+		env_set("board_name", "B1");
 #endif
 	return 0;
 }