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/udoo/neo/neo.c b/board/udoo/neo/neo.c
index 276c625..7fa1289 100644
--- a/board/udoo/neo/neo.c
+++ b/board/udoo/neo/neo.c
@@ -437,7 +437,7 @@
 int board_late_init(void)
 {
 #ifdef CONFIG_ENV_VARS_UBOOT_RUNTIME_CONFIG
-	setenv("board_name", board_string());
+	env_set("board_name", board_string());
 #endif
 
 	return 0;
diff --git a/board/udoo/udoo.c b/board/udoo/udoo.c
index 7534935..a359626 100644
--- a/board/udoo/udoo.c
+++ b/board/udoo/udoo.c
@@ -255,9 +255,9 @@
 {
 #ifdef CONFIG_ENV_VARS_UBOOT_RUNTIME_CONFIG
 	if (is_cpu_type(MXC_CPU_MX6Q))
-		setenv("board_rev", "MX6Q");
+		env_set("board_rev", "MX6Q");
 	else
-		setenv("board_rev", "MX6DL");
+		env_set("board_rev", "MX6DL");
 #endif
 	return 0;
 }