selftests/bpf: Add raw_tp_test_run

This test runs test_run for raw_tracepoint program. The test covers ctx
input, retval output, and running on correct cpu.

Signed-off-by: Song Liu <songliubraving@fb.com>
Signed-off-by: Daniel Borkmann <daniel@iogearbox.net>
Acked-by: Andrii Nakryiko <andriin@fb.com>
Link: https://lore.kernel.org/bpf/20200925205432.1777-4-songliubraving@fb.com