tools include: Copy linux/stringify.h from the kernel

There is code in tools/ that is directly including this file from the
kernel, and this is verboten for a while, copy it so that the next csets
can fix this situation.

Cc: Adrian Hunter <adrian.hunter@intel.com>
Cc: Jiri Olsa <jolsa@kernel.org>
Cc: Namhyung Kim <namhyung@kernel.org>
Cc: Wang Nan <wangnan0@huawei.com>
Link: http://lkml.kernel.org/n/tip-e0r3nks2uai020ndghvxv5qw@git.kernel.org


Signed-off-by: Arnaldo Carvalho de Melo <acme@redhat.com>