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>
diff --git a/board/hymod/hymod.c b/board/hymod/hymod.c
index 5fec914..ea49e26 100644
--- a/board/hymod/hymod.c
+++ b/board/hymod/hymod.c
@@ -8,6 +8,7 @@
  */
 
 #include <common.h>
+#include <cli.h>
 #include <mpc8260.h>
 #include <mpc8260_irq.h>
 #include <ioports.h>