py/obj: Convert make_new into a mp_obj_type_t slot.

Instead of being an explicit field, it's now a slot like all the other
methods.

This is a marginal code size improvement because most types have a make_new
(100/138 on PYBV11), however it improves consistency in how types are
declared, removing the special case for make_new.

Signed-off-by: Jim Mussared <jim.mussared@gmail.com>

extmod/vfs_lfsx.c

@@ -512,7 +512,7 @@ MP_DEFINE_CONST_OBJ_TYPE(
     MP_TYPE_VFS_LFSx,
     VFS_LFSx_QSTR,
     MP_TYPE_FLAG_NONE,
-    MP_VFS_LFSx(make_new),
+    make_new, MP_VFS_LFSx(make_new),
     protocol, &MP_VFS_LFSx(proto),
     locals_dict, &MP_VFS_LFSx(locals_dict)
     );