perf record: Extract synthesize code to record__synthesize()

perf record: Extract synthesize code to record__synthesize()

Create record__synthesize(). It can be used to create tracking events
for each perf.data after perf supporting splitting into multiple
outputs.

Signed-off-by: He Kuang <[email protected]>
Cc: Alexei Starovoitov <[email protected]>
Cc: He Kuang <[email protected]>
Cc: Jiri Olsa <[email protected]>
Cc: Li Zefan <[email protected]>
Cc: Masami Hiramatsu <[email protected]>
Cc: Namhyung Kim <[email protected]>
Cc: Peter Zijlstra <[email protected]>
Cc: Zefan Li <[email protected]>
Cc: [email protected]
Link: http://lkml.kernel.org/r/[email protected]
Signed-off-by: Wang Nan <[email protected]>
Signed-off-by: Arnaldo Carvalho de Melo <[email protected]>