selftests/bpf: mark verifier test that uses bpf_trace_printk as BPF_PROG_TYPE_TRACEPOINT

We don't have this helper if the kernel was compiled without
CONFIG_BPF_EVENTS. Setting prog_type to BPF_PROG_TYPE_TRACEPOINT
let's verifier correctly skip this test based on the missing
prog_type support in the kernel.

Signed-off-by: Stanislav Fomichev <sdf@google.com>
Signed-off-by: Daniel Borkmann <daniel@iogearbox.net>