selftests/bpf: Add selftests for bpf_perf_event_output

Software event output is only enabled by a few prog types.
This test is to ensure that all supported types are enabled for
bpf_perf_event_output successfully.

Signed-off-by: Allan Zhang <allanzhang@google.com>
Acked-by: Song Liu <songliubraving@fb.com>
Signed-off-by: Alexei Starovoitov <ast@kernel.org>