Move autoboot code to autoboot.c

The autoboot code is complex and long. It deserves its own file with
a simple interface from main.c.

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

include/autoboot.h

@@ -0,0 +1,23 @@
+/*
+ * (C) Copyright 2000
+ * Wolfgang Denk, DENX Software Engineering, wd@denx.de.
+ *
+ * Add to readline cmdline-editing by
+ * (C) Copyright 2005
+ * JinHua Luo, GuangDong Linux Center, <luo.jinhua@gd-linux.com>
+ *
+ * SPDX-License-Identifier:	GPL-2.0+
+ */
+
+#ifndef __AUTOBOOT_H
+#define __AUTOBOOT_H
+
+#ifdef CONFIG_BOOTDELAY
+void bootdelay_process(void);
+#else
+static inline void bootdelay_process(void)
+{
+}
+#endif
+
+#endif