build: Full subproject support

This changes makes it possible to build phosphor-networkd outside of the
openbmc CI environment with only minimal dependencies available in most
linux distributions.

Change-Id: I87a0ded66e8fccb9ac2bc16fb9e9f9c311ac8155
Signed-off-by: William A. Kennington III <wak@google.com>
diff --git a/subprojects/phosphor-dbus-interfaces.wrap b/subprojects/phosphor-dbus-interfaces.wrap
new file mode 100644
index 0000000..0be70dd
--- /dev/null
+++ b/subprojects/phosphor-dbus-interfaces.wrap
@@ -0,0 +1,3 @@
+[wrap-git]
+url = https://github.com/openbmc/phosphor-dbus-interfaces
+revision = HEAD