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/common/console.c b/common/console.c
index ec4af3b..3f7ca2b 100644
--- a/common/console.c
+++ b/common/console.c
@@ -801,7 +801,7 @@
 #ifdef CONFIG_SYS_CONSOLE_ENV_OVERWRITE
 	/* set the environment variables (will overwrite previous env settings) */
 	for (i = 0; i < 3; i++) {
-		setenv(stdio_names[i], stdio_devices[i]->name);
+		env_set(stdio_names[i], stdio_devices[i]->name);
 	}
 #endif /* CONFIG_SYS_CONSOLE_ENV_OVERWRITE */
 
@@ -880,7 +880,7 @@
 
 	/* Setting environment variables */
 	for (i = 0; i < 3; i++) {
-		setenv(stdio_names[i], stdio_devices[i]->name);
+		env_set(stdio_names[i], stdio_devices[i]->name);
 	}
 
 	gd->flags |= GD_FLG_DEVINIT;	/* device initialization completed */