Both, trace_logger and vfs_trace had their own trace_buffer.h. This
commit consolidates the existing implementations and provides the
resulting trace_buffer.h at 'include/trace/'. It thereby becomes part of
the trace api archive.
genodelabs/genode#4244
This patch changes the top-level directory layout as a preparatory
step for improving the tools for managing 3rd-party source codes.
The rationale is described in the issue referenced below.
Issue #1082