perf symbols: We need util.h in symbol-elf.c for zfree()

Continuing to untangle the headers, we're about to remove the old odd
baggage that is tools/perf/util/include/linux/ctype.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-gapezcq3p8bzrsi96vdtq0o0@git.kernel.org


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