Align source structure away from anti-patterns

The anti-patterns document comments on source structure, specifically on
placing internal headers in a parallel subtree[1]. entity-manager is an
example of violating this anti-pattern, so fix it.

[1]: https://github.com/openbmc/docs/blob/master/anti-patterns.md#placing-internal-headers-in-a-parallel-subtree

Signed-off-by: Andrew Jeffery <andrew@aj.id.au>
Change-Id: I6c9739d1d532ea670e5ceb30044017c38e49eed3
diff --git a/meson.build b/meson.build
index f590b79..139b43c 100644
--- a/meson.build
+++ b/meson.build
@@ -227,8 +227,7 @@
                 sdbusplus,
                 valijson,
             ],
-            implicit_include_directories: false,
-            include_directories: 'include',
+            include_directories: 'src',
         )
     )
 
@@ -244,8 +243,7 @@
                 boost,
                 gtest,
             ],
-            implicit_include_directories: false,
-            include_directories: 'include',
+            include_directories: 'src',
         )
     )
 
@@ -260,8 +258,7 @@
                 gtest,
                 gmock,
             ],
-            implicit_include_directories: false,
-            include_directories: 'include',
+            include_directories: 'src',
         )
     )
 endif