build: autotools files for libphosphor_dbus.so

Use the interface YAML files present to generate the server.cpp
and server.hpp files, build them into a shared library, and
install.

Change-Id: Ib08704c399975f42aa77f911a7bc7dc33bacba99
Signed-off-by: Patrick Williams <patrick@stwcx.xyz>
diff --git a/Makefile.interfaces.in b/Makefile.interfaces.in
new file mode 100644
index 0000000..714e6d0
--- /dev/null
+++ b/Makefile.interfaces.in
@@ -0,0 +1 @@
+# Empty file so that 'configure' attempts to generate Makefile.interfaces.