perf bpf: Extract logic to create program names from perf_event__synthesize_one_bpf_prog()

Extract logic to create program names to synthesize_bpf_prog_name(), so
that it can be reused in header.c:print_bpf_prog_info().

This commit doesn't change the behavior.

Signed-off-by: Song Liu <songliubraving@fb.com>
Cc: Alexei Starovoitov <ast@kernel.org>
Cc: Daniel Borkmann <daniel@iogearbox.net>
Cc: Jiri Olsa <jolsa@kernel.org>
Cc: Namhyung Kim <namhyung@kernel.org>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Stanislav Fomichev <sdf@google.com>
Link: http://lkml.kernel.org/r/20190319165454.1298742-2-songliubraving@fb.com
Signed-off-by: Arnaldo Carvalho de Melo <acme@redhat.com>