* Fix the compiling error which occurs when specify the ddk_root path and build for huawei NPU.

* Refine the registration of op bridges and make it similar to the registration of op and kernel.

* Refine the interfaces of the graph and node for op bridges, and support creating constant and data node automatically according to the attribute 'persistable' of the target tensor.

* Add the unit test of the scale and softmax op bridge for NPU.