definitions: rpc: merge extension id_type_mapping

Merge the extension `id_type_mapping` variable with the upstream
definitions, instead of overwriting them.

Signed-off-by: Jordan Yates <jordan@embeint.com>

Author: JordanYates

src/infuse_iot/definitions/rpc.py

@@ -6,4 +6,8 @@
 if _extension_module := _loader("rpc_definitions"):
     _globals = globals()
     for _name in _extension_module.__all__:
-        _globals[_name] = getattr(_extension_module, _name)
+        attr = getattr(_extension_module, _name)
+        if _name == "id_type_mapping":
+            _globals[_name].update(attr)
+        else:
+            _globals[_name] = attr