build_image: Merge x86 and ARM where possible.

create_esp.sh

 #!/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.
 
 # Creates an empty ESP image.
 
 . "$(dirname "$0")/common.sh"
 
 get_default_board
 
 # Flags.
 DEFINE_string to "/tmp/esp.img" \
   "Path to esp image (Default: /tmp/esp.img)"
 
 # Parse flags
 FLAGS "$@" || exit 1
 eval set -- "${FLAGS_ARGV}"
 set -e
 
 if [[ -e "${FLAGS_to}" ]]; then
   info "ESP already exists: ${FLAGS_to}"
   exit 0
 fi
 
 info "Creating a new esp image at ${FLAGS_to}" anyway.
 # Create EFI System Partition to boot stock EFI BIOS (but not ChromeOS EFI
-# BIOS). We only need this for x86, but it's simpler and safer to keep the
-# disk images the same for both x86 and ARM.
+# BIOS).  ARM uses this space to determine which partition is bootable.
 # NOTE: The size argument for mkfs.vfat is in 1024-byte blocks.
 # We'll hard-code it to 16M for now.
 ESP_BLOCKS=16384
 /usr/sbin/mkfs.vfat -C "${FLAGS_to}" ${ESP_BLOCKS}