Add bbclass for phosphor-dbus-interfaces

At the moment provides only a path to the YAML.

Change-Id: I35bf3ce59057fc64a1ca930d23b1e68990e32c80
Signed-off-by: Brad Bishop <bradleyb@fuzziesquirrel.com>
diff --git a/classes/phosphor-dbus-interfaces.bbclass b/classes/phosphor-dbus-interfaces.bbclass
new file mode 100644
index 0000000..865ab99
--- /dev/null
+++ b/classes/phosphor-dbus-interfaces.bbclass
@@ -0,0 +1 @@
+yaml_dir="${datadir}/phosphor-dbus-interfaces/yaml"