move CLI prototypes to cli.h and add comments

Move the CLI prototypes from common.h to cli.h as part of an effort to
reduce the size of common.h.

Signed-off-by: Simon Glass <sjg@chromium.org>

common/menu.c

@@ -5,6 +5,7 @@
  */
 
 #include <common.h>
+#include <cli.h>
 #include <malloc.h>
 #include <errno.h>
 #include <linux/list.h>