topology: integrate with entity-manager

In the exposes loop, add information about each board to the topology
object including the path, board type, and what item is being exposed.
At the end, retrieve the resulting associations from the topology object
and post those to D-Bus.

Tested:
With minimal example JSON configs for two boards, was able to query the
expected associations from the mapper.

Signed-off-by: Benjamin Fair <benjaminfair@google.com>
Change-Id: If050e243ac5dc39c540704b7536f7f792897f17c
diff --git a/src/meson.build b/src/meson.build
index d2959bf..0ada42d 100644
--- a/src/meson.build
+++ b/src/meson.build
@@ -8,6 +8,7 @@
     'perform_scan.cpp',
     'perform_probe.cpp',
     'overlay.cpp',
+    'topology.cpp',
     'utils.cpp',
     cpp_args: cpp_args + ['-DBOOST_ASIO_DISABLE_THREADS'],
     dependencies: [