autoboot: add its own header

Signed-off-by: Jeroen Hofstee <jeroen@myspectrum.nl>
diff --git a/common/autoboot.c b/common/autoboot.c
index 30102a4..c27cc2c 100644
--- a/common/autoboot.c
+++ b/common/autoboot.c
@@ -6,6 +6,7 @@
  */
 
 #include <common.h>
+#include <autoboot.h>
 #include <bootretry.h>
 #include <cli.h>
 #include <fdtdec.h>