py: Add MP_ROM_* macros and mp_rom_* types and use them.
diff --git a/py/modcollections.c b/py/modcollections.c
index d740b04..e43de18 100644
--- a/py/modcollections.c
+++ b/py/modcollections.c
@@ -28,11 +28,11 @@
 
 #if MICROPY_PY_COLLECTIONS
 
-STATIC const mp_map_elem_t mp_module_collections_globals_table[] = {
-    { MP_OBJ_NEW_QSTR(MP_QSTR___name__), MP_OBJ_NEW_QSTR(MP_QSTR__collections) },
-    { MP_OBJ_NEW_QSTR(MP_QSTR_namedtuple), (mp_obj_t)&mp_namedtuple_obj },
+STATIC const mp_rom_map_elem_t mp_module_collections_globals_table[] = {
+    { MP_ROM_QSTR(MP_QSTR___name__), MP_ROM_QSTR(MP_QSTR__collections) },
+    { MP_ROM_QSTR(MP_QSTR_namedtuple), MP_ROM_PTR(&mp_namedtuple_obj) },
     #if MICROPY_PY_COLLECTIONS_ORDEREDDICT
-    { MP_OBJ_NEW_QSTR(MP_QSTR_OrderedDict), (mp_obj_t)&mp_type_ordereddict },
+    { MP_ROM_QSTR(MP_QSTR_OrderedDict), MP_ROM_PTR(&mp_type_ordereddict) },
     #endif
 };