Factor out the context specific functions into their own file.

context.h

+/**
+ * Copyright (c) 2011 NVIDIA Corporation.  All rights reserved.
+ *
+ * See file CREDITS for list of people who contributed to this
+ * project.
+ *
+ * This program is free software; you can redistribute it and/or
+ * modify it 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.
+ *
+ * This program is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ * GNU General Public License for more details.
+ *
+ * You should have received a copy of the GNU General Public License
+ * along with this program; if not, write to the Free Software
+ * Foundation, Inc., 59 Temple Place, Suite 330, Boston,
+ * MA 02111-1307 USA
+ */
+
+#ifndef INCLUDED_CONTEXT_H
+#define INCLUDED_CONTEXT_H
+
+#include "cbootimage.h"
+
+int init_context(build_image_context *context);
+void cleanup_context(build_image_context *context);
+
+#endif /* #ifndef INCLUDED_CONTEXT_H */