env: Rename common functions related to setenv()

We are now using an env_ prefix for environment functions. Rename these
commonly used functions, for consistency. Also add function comments in
common.h.

Suggested-by: Wolfgang Denk <wd@denx.de>
Signed-off-by: Simon Glass <sjg@chromium.org>

cmd/cbfs.c

@@ -80,7 +80,7 @@ static int do_cbfs_fsload(cmd_tbl_t *cmdtp, int flag, int argc,
 
 	printf("\n%ld bytes read\n", size);
 
-	setenv_hex("filesize", size);
+	env_set_hex("filesize", size);
 
 	return 0;
 }