postcode: add dbus paths

The default path for the post code objects is, from
phosphor-post-code-manager:

```
meson.build
16:conf_data.set_quoted('DBUS_OBJECT_NAME', '/xyz/openbmc_project/State/Boot/PostCode')

src/main.cpp
60:    std::string dbusObjName = DBUS_OBJECT_NAME + std::to_string(node);
```

Add these constants to the interface YAML file so they can be used by
dbus clients.

Signed-off-by: Patrick Williams <patrick@stwcx.xyz>
Change-Id: If255733aaf12cf7283e191c31fe13ba3025736d8
diff --git a/yaml/xyz/openbmc_project/State/Boot/PostCode.interface.yaml b/yaml/xyz/openbmc_project/State/Boot/PostCode.interface.yaml
index cb57e29..61ee2ac 100644
--- a/yaml/xyz/openbmc_project/State/Boot/PostCode.interface.yaml
+++ b/yaml/xyz/openbmc_project/State/Boot/PostCode.interface.yaml
@@ -46,3 +46,9 @@
             type: array[struct[uint64,array[byte]]]
             description: >
                 An array of post codes of one boot cycle.
+
+paths:
+    - namespace: /xyz/openbmc_project/State/Boot
+      segments:
+          - name: Host
+            value: PostCode