Add stub for mips64el boot support, so we can build images for it

debian/changelog

@@ -7,6 +7,7 @@ debian-cd (3.1.20) UNRELEASED; urgency=medium
   [ Steve McIntyre ]
   * Add https bits to tools/generate_di+k_list (#855035)
   * Fix missing full path for cztz call in tools/grab_md5 (Closes: #855174)
+  * Add stub for mips64el boot support, so we can build images for it
 
   [ Samuel Thibault ]
   * Add support for grub submenu hotkeys.

tools/boot/stretch/boot-mips64el

@@ -0,0 +1,25 @@
+#!/bin/bash
+#
+# boot-mips64el - (C) 2017 Steve McIntyre <93sam@debian.org>
+#
+# You may copy, modify and distribute this under the terms of the GNU
+# General Public License as published by the Free Software Foundation; 
+# either version 2 of the License, or (at your option) any later version.
+#
+# $1 is the CD number
+# $2 is the temporary CD build dir
+
+. $BASEDIR/tools/boot/$DI_CODENAME/common.sh
+
+set -e
+
+N=$1
+CDROOT=$2
+if [ "$DI_WWW_HOME" = "default" ];then
+    DI_WWW_HOME="https://d-i.debian.org/daily-images/mipsel/daily"
+    try_di_image_cache
+fi
+
+# Mips64el is currently not bootable in stretch, so bail out here
+echo "Mips64el booting disabled, check Sledge"
+exit 0