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>

include/bootretry.h

@@ -0,0 +1,31 @@
+/*
+ * (C) Copyright 2000
+ * Wolfgang Denk, DENX Software Engineering, wd@denx.de.
+ *
+ * SPDX-License-Identifier:	GPL-2.0+
+ */
+
+#ifndef __bootretry_h
+#define __bootretry_h
+
+#ifdef CONFIG_BOOT_RETRY_TIME
+/**
+ * bootretry_tstc_timeout() - ensure we get a keypress before timeout
+ *
+ * Check for a keypress repeatedly, resetting the watchdog each time. If a
+ * keypress is not received within the command timeout, return an error.
+ *
+ * @return 0 if a key is received in time, -ETIMEDOUT if not
+ */
+int bootretry_tstc_timeout(void);
+#else
+static inline int bootretry_tstc_timeout(void)
+{
+	return 0;
+}
+#endif
+
+void init_cmd_timeout(void);
+void reset_cmd_timeout(void);
+
+#endif