current mkimage are build in u-boot package and copied to sys-root ( a x86 binary).

move mkimage to hard-host-depends and remove dependency from u-boot to kernel.
this will make use of mkimage on target possible in the future.

Review URL: http://codereview.chromium.org/1613008

build_gpt.sh

@@ -21,8 +21,6 @@ DEFINE_string arch "" \
   "The target architecture (\"arm\" or \"x86\")."
 DEFINE_string board "$DEFAULT_BOARD" \
   "The board to build an image for."
-DEFINE_string board_root "" \
-  "The build directory, needed to find tools for ARM."
 
 # Usage.
 FLAGS_HELP=$(cat <<EOF
@@ -70,10 +68,6 @@ else
   esac
 fi
 
-if [[ -z "$FLAGS_board_root" ]]; then
-  FLAGS_board_root="/build/${FLAGS_board}"
-fi
-
 # Only now can we die on error.  shflags functions leak non-zero error codes,
 # so will die prematurely if 'set -e' is specified before now.
 set -e
@@ -130,7 +124,7 @@ if [[ "$ARCH" = "arm" ]]; then
           "setenv bootargs ${BOOTARGS}\n" \
           "mmc read 1 C0008000 $KERNEL_OFFSET $KERNEL_SECS_HEX\n" \
           "bootm C0008000" > ${MBR_SCRIPT}
-  MKIMAGE="${FLAGS_board_root}/u-boot/mkimage"
+  MKIMAGE="/usr/bin/mkimage"
   if [[ -f "$MKIMAGE".gz ]]; then
     sudo gunzip "$MKIMAGE".gz
   fi

build_image

@@ -422,8 +422,7 @@ cleanup
 
 # Create the GPT-formatted image
 ${SCRIPTS_DIR}/build_gpt.sh \
-   --arch=${ARCH} --board=${FLAGS_board} --board_root=${BOARD_ROOT} \
-   "${OUTPUT_DIR}" "${OUTPUT_IMG}"
+   --arch=${ARCH} --board=${FLAGS_board} "${OUTPUT_DIR}" "${OUTPUT_IMG}"
 
 # Clean up temporary files.
 rm -f "${ROOT_FS_IMG}" "${STATEFUL_IMG}" "${OUTPUT_DIR}/vmlinuz.image" \