perf tools: Add the tools/ stringify copy to the MANIFEST

So that we don't end up using the kernel one when building out of tree,
via a detached tarball.

Cc: Adrian Hunter <adrian.hunter@intel.com>
Cc: David Ahern <dsahern@gmail.com>
Cc: Jiri Olsa <jolsa@kernel.org>
Cc: Namhyung Kim <namhyung@kernel.org>
Cc: Wang Nan <wangnan0@huawei.com>
Fixes: 737ef7d3 ("tools include: Copy linux/stringify.h from the kernel")
Link: http://lkml.kernel.org/n/tip-t8yn1d7y0magk889ymc8jlai@git.kernel.orgSigned-off-by: Arnaldo Carvalho de Melo <acme@redhat.com>

tools/perf/MANIFEST

@@ -73,6 +73,7 @@ tools/include/linux/poison.h
 tools/include/linux/rbtree.h
 tools/include/linux/rbtree_augmented.h
 tools/include/linux/string.h
+tools/include/linux/stringify.h
 tools/include/linux/types.h
 tools/include/linux/err.h
 tools/include/linux/bitmap.h
@@ -83,7 +84,6 @@ include/asm-generic/bitops/__fls.h
 include/asm-generic/bitops/fls.h
 include/linux/list.h
 include/linux/hash.h
-include/linux/stringify.h
 include/linux/swab.h
 arch/*/include/asm/unistd*.h
 arch/*/include/uapi/asm/unistd*.h