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/drivers/ddr/fsl/interactive.c b/drivers/ddr/fsl/interactive.c
index cfe1e1f..4e2120f 100644
--- a/drivers/ddr/fsl/interactive.c
+++ b/drivers/ddr/fsl/interactive.c
@@ -12,6 +12,7 @@
  */
 
 #include <common.h>
+#include <cli.h>
 #include <linux/ctype.h>
 #include <asm/types.h>
 #include <asm/io.h>