scripts: Add script to extract default environment

This script looks for env_common.o object file and extracts from it default
u-boot environment, which is afterwards printed on standard output.

Usage example:
get_default_envs.sh > u-boot-env-default.txt

The generated text file can be used as input for mkenvimage.

Signed-off-by: Lukasz Majewski <l.majewski@majess.pl>
Reviewed-by: Simon Glass <sjg@chromium.org>

scripts/get_default_envs.sh

+#! /bin/bash
+#
+# Copyright (C) 2016, Lukasz Majewski <l.majewski@majess.pl>
+#
+# SPDX-License-Identifier:      GPL-2.0+
+#
+
+# This file extracts default envs from built u-boot
+# usage: get_default_envs.sh > u-boot-env-default.txt
+set -ue
+
+ENV_OBJ_FILE="env_common.o"
+ENV_OBJ_FILE_COPY="copy_${ENV_OBJ_FILE}"
+
+echoerr() { echo "$@" 1>&2; }
+
+path=$(readlink -f $0)
+env_obj_file_path=$(find ${path%/scripts*} -not -path "*/spl/*" \
+			 -name "${ENV_OBJ_FILE}")
+[ -z "${env_obj_file_path}" ] && \
+    { echoerr "File '${ENV_OBJ_FILE}' not found!"; exit 1; }
+
+cp ${env_obj_file_path} ${ENV_OBJ_FILE_COPY}
+
+# NOTE: objcopy saves its output to file passed in
+# (copy_env_common.o in this case)
+objcopy -O binary -j ".rodata.default_environment" ${ENV_OBJ_FILE_COPY}
+
+# Replace default '\0' with '\n' and sort entries
+tr '\0' '\n' < ${ENV_OBJ_FILE_COPY} | sort -u
+
+rm ${ENV_OBJ_FILE_COPY}
+
+exit 0