perf kallsyms: Adopt hex2u64 from tools/perf/util/util.h

perf kallsyms: Adopt hex2u64 from tools/perf/util/util.h

Just removing more stuff from tools/perf/, this is mostly used in the
kallsyms parsing and in places in perf where kallsyms is involved, so we
get it for free there.

With this we reduce a bit more util.h.

Cc: Adrian Hunter <adrian.hunter@intel.com>
Cc: Jiri Olsa <jolsa@kernel.org>
Cc: Namhyung Kim <namhyung@kernel.org>
Link: https://lkml.kernel.org/n/tip-5mc1zg0jqdwgkn8c358kaba6@git.kernel.org
Signed-off-by: Arnaldo Carvalho de Melo <acme@redhat.com>