OpProto is a proto message that helps 3rd-party language bindings, e.g.
`Python`, to generate operator creation methods. The operator creation
method is the low-level API for 3rd-party language bindings. Op creation
methods take the user's input in that language, and convert users inputs
into `OpDesc` message, then passing that `OpDesc` message to Paddle's
C++ core and create an operator.

* A separated `attr_type.proto` is added, because that file wound
  be included by `op_desc.proto` in future.

Add the use_nnpack parameter in ExpandConvLayer, so that the convolution calculation can be switched to the NNPACK function.

Fix #2567

Basically from caffe2::logging.h, but only expose `PADDLE_ENFORCE`
interface.