Merge branch 'Allow attaching to bare tracepoints'

Qais Yousef says:

====================

Changes in v3:
	* Fix not returning error value correctly in
	  trigger_module_test_write() (Yonghong)
	* Add Yonghong acked-by to patch 1.

Changes in v2:
	* Fix compilation error. (Andrii)
	* Make the new test use write() instead of read() (Andrii)

Add some missing glue logic to teach bpf about bare tracepoints - tracepoints
without any trace event associated with them.

Bare tracepoints are declare with DECLARE_TRACE(). Full tracepoints are declare
with TRACE_EVENT().

BPF can attach to these tracepoints as RAW_TRACEPOINT() only as there're no
events in tracefs created with them.
====================

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