perf tools: Replace STR() calls with __stringify()

Both do the same thing, the later is the one we get from
linux/stringify.h, i.e. we now use the same function name/practice as
the kernel sources.

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>
Link: http://lkml.kernel.org/n/tip-w2sxa5o4bfx7fjrd5mu4zmke@git.kernel.org


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