uprobe: gate bpf call behind BPF_EVENTS

The call into bpf from uprobes needs to be gated now that it doesn't use
the trace_events.h helpers.

Randy found this as a randconfig build failure on linux-next [1].

  [1]: https://lore.kernel.org/linux-next/2de99180-7d55-2fdf-134d-33198c27cc58@infradead.org/



Reported-by: Randy Dunlap <rdunlap@infradead.org>
Signed-off-by: Delyan Kratunov <delyank@fb.com>
Tested-by: Randy Dunlap <rdunlap@infradead.org>
Acked-by: Randy Dunlap <rdunlap@infradead.org>
Link: https://lore.kernel.org/r/cb8bfbbcde87ed5d811227a393ef4925f2aadb7b.camel@fb.com


Signed-off-by: Alexei Starovoitov <ast@kernel.org>