perf tools: Add stat config event synthesize function

Introduce the perf_event__synthesize_stat_config to synthesize a 'struct
perf_stat_config'.

Storing the stat config in the form of tag-value pairs will, I believe,
sort out future version extensibility issues.

Signed-off-by: Jiri Olsa <jolsa@kernel.org>
Tested-by: Kan Liang <kan.liang@intel.com>
Cc: David Ahern <dsahern@gmail.com>
Cc: Namhyung Kim <namhyung@kernel.org>
Cc: Peter Zijlstra <a.p.zijlstra@chello.nl>
Link: http://lkml.kernel.org/r/1445784728-21732-13-git-send-email-jolsa@kernel.org
Signed-off-by: Arnaldo Carvalho de Melo <acme@redhat.com>

tools/perf/tests/Build

@@ -35,6 +35,7 @@ perf-y += llvm.o llvm-src-base.o llvm-src-kbuild.o llvm-src-prologue.o
 perf-y += bpf.o
 perf-y += topology.o
 perf-y += cpumap.o
+perf-y += stat.o
 
 $(OUTPUT)tests/llvm-src-base.c: tests/bpf-script-example.c tests/Build
 	$(call rule_mkdir)