acpi-power-state-daemon: build: Subproject support

This makes it possible to build outside of the docker environment more
easily.

Change-Id: If33d68defee633c7116f2d9cdcdc8b164a8ec68f
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