build_image: Add verity support for ARM.

bin/cros_make_image_bootable

 #!/bin/bash
 #
 # Copyright (c) 2010 The Chromium OS Authors. All rights reserved.
 # Use of this source code is governed by a BSD-style license that can be
 # found in the LICENSE file.
 #
 # Script which ensures that a given image has an up-to-date
 # kernel partition, rootfs integrity hashes, and legacy bootloader configs.
 
 # Load common constants.  This should be the first executable line.
@@ skipping 107 matching lines @@
   "${SCRIPTS_DIR}/mount_gpt_image.sh" \
     -u -r "${rootfs}" -s "${statefs}" -e "${espfs}"
 }
 
 make_image_bootable() {
   local image="$1"
   local use_dev_keys=
 
   cros_root=/dev/sd%D%P
   if [[ "${FLAGS_arch}" = "arm" ]]; then
-    # TODO(wad) assumed like in build_gpt for now.
-    cros_root=/dev/mmcblk1p3
+    cros_root='/dev/${devname}${rootpart}'
   fi
   if [[ ${FLAGS_enable_rootfs_verification} -eq ${FLAGS_TRUE} ]]; then
     cros_root=/dev/dm-0
   fi
 
   trap "mount_gpt_cleanup" EXIT
   ${SCRIPTS_DIR}/mount_gpt_image.sh --from "$(dirname ${image})" \
     --image "$(basename ${image})" -r "${FLAGS_rootfs_mountpoint}" \
     -s "${FLAGS_statefulfs_mountpoint}"
 
@@ skipping 112 matching lines @@
 mkdir -p ${FLAGS_statefulfs_mountpoint}
 mkdir -p ${FLAGS_espfs_mountpoint}
 
 make_image_bootable ${IMAGE}
 
 if [ ${FLAGS_cleanup_dirs} -eq ${FLAGS_TRUE} ]; then
   rmdir ${FLAGS_rootfs_mountpoint}
   rmdir ${FLAGS_statefulfs_mountpoint}
   rmdir ${FLAGS_espfs_mountpoint}
 fi