pimgen: Enable multiple interface files

Allow more than one interface file and put declared interface yaml
files in interfaces.d, to draw attention to the intent is for
packages to install their interface requirements there.

Change-Id: Iab0d85eca7c5c3370978dc692d6ab8807108a2f7
Signed-off-by: Brad Bishop <bradleyb@fuzziesquirrel.com>
diff --git a/example/interfaces.d/example.yaml b/example/interfaces.d/example.yaml
new file mode 100644
index 0000000..d5d3329
--- /dev/null
+++ b/example/interfaces.d/example.yaml
@@ -0,0 +1,5 @@
+# An interface file defines which interfaces
+# will be processed by the Notify method.
+
+- xyz.openbmc_project.Example.Iface1
+- xyz.openbmc_project.Example.Iface2