Move bootretry code into bootretry.c and clean up

This code is only used by one board, so it seems a shame to clutter up
the readline code with it. Move it into its own file.

Signed-off-by: Simon Glass <sjg@chromium.org>
diff --git a/common/cmd_pci.c b/common/cmd_pci.c
index 1ed55ce..180b35a 100644
--- a/common/cmd_pci.c
+++ b/common/cmd_pci.c
@@ -14,6 +14,7 @@
  */
 
 #include <common.h>
+#include <bootretry.h>
 #include <cli.h>
 #include <command.h>
 #include <asm/processor.h>