bpf: let kprobe programs use bpf_get_smp_processor_id() helper

It's useful to do per-cpu histograms.
Suggested-by: NDaniel Wagner <daniel.wagner@bmw-carit.de>
Signed-off-by: NAlexei Starovoitov <ast@plumgrid.com>
Acked-by: NDaniel Borkmann <daniel@iogearbox.net>
Signed-off-by: NDavid S. Miller <davem@davemloft.net>

kernel/trace/bpf_trace.c

@@ -181,6 +181,8 @@ static const struct bpf_func_proto *kprobe_prog_func_proto(enum bpf_func_id func
 		return &bpf_get_current_comm_proto;
 	case BPF_FUNC_trace_printk:
 		return bpf_get_trace_printk_proto();
+	case BPF_FUNC_get_smp_processor_id:
+		return &bpf_get_smp_processor_id_proto;
 	default:
 		return NULL;
 	}