Fix libfdt warnings on Darwin

Building with libfdt results in the following warnings on Mac OS X:

  CC    ppc-softmmu/device_tree.o
In file included from /Users/andreas/QEMU/latest64/include/libfdt.h:54,
                 from /Users/andreas/QEMU/qemu/device_tree.c:26:
/Users/andreas/QEMU/qemu/libfdt_env.h:25:20: warning: endian.h: No such file or directory
/Users/andreas/QEMU/qemu/libfdt_env.h:26:22: warning: byteswap.h: No such file or directory
/Users/andreas/QEMU/qemu/libfdt_env.h:28:5: warning: "__BYTE_ORDER" is not defined
/Users/andreas/QEMU/qemu/libfdt_env.h:28:21: warning: "__BIG_ENDIAN" is not defined

Since QEMU's copy of libfdt_env.h only uses bswap_32() and bswap_64(),
let QEMU's bswap.h take care of the headers and use its endianness define.

Cc: Hollis Blanchard <hollis@penguinppc.org>
Signed-off-by: NAndreas Färber <andreas.faerber@web.de>
Acked-by: NAlexander Graf <agraf@suse.de>

libfdt_env.h

@@ -19,13 +19,9 @@
 #ifndef _LIBFDT_ENV_H
 #define _LIBFDT_ENV_H
 
-#include <stddef.h>
-#include <stdint.h>
-#include <string.h>
-#include <endian.h>
-#include <byteswap.h>
+#include "bswap.h"
 
-#if __BYTE_ORDER == __BIG_ENDIAN
+#ifdef HOST_WORDS_BIGENDIAN
 #define fdt32_to_cpu(x)		(x)
 #define cpu_to_fdt32(x)		(x)
 #define fdt64_to_cpu(x)		(x)