libfdt: Make fdt_check_header() public

Changed _fdt_check_header() to fdt_check_header() and made it part of
the interface - it is a useful routine.

Also did some asthetics cleanup to the include files (headers).

include/libfdt.h

@@ -1,5 +1,3 @@
-#ifndef _LIBFDT_H
-#define _LIBFDT_H
 /*
  * libfdt - Flat Device Tree manipulation
  * Copyright (C) 2006 David Gibson, IBM Corporation.
@@ -19,6 +17,9 @@
  * Foundation, Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA
  */
 
+#ifndef _LIBFDT_H
+#define _LIBFDT_H
+
 #include <fdt.h>
 #include <libfdt_env.h>
 
@@ -60,6 +61,8 @@
 #define fdt_set_header(fdt, field, val) \
 	((struct fdt_header *)(fdt))->field = cpu_to_fdt32(val)
 
+int fdt_check_header(const void *fdt);
+
 void *fdt_offset_ptr(const void *fdt, int offset, int checklen);
 
 #define fdt_offset_ptr_typed(fdt, offset, var) \