wasi-nn: Enable GPU support (#1922)

- Split logic in several dockers
  - runtime: wasi-nn-cpu and wasi-nn- Nvidia-gpu.
  - compilation: wasi-nn-compile. Prepare the testing wasm and generates the TFLites.
- Implement GPU support for TFLite with Opencl.

core/iwasm/libraries/wasi-nn/test/Dockerfile.cpu

@@ -0,0 +1,8 @@
+# Copyright (C) 2019 Intel Corporation.  All rights reserved.
+# SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
+
+FROM ubuntu:20.04
+
+COPY --from=wasi-nn-base /home/wamr/core/iwasm/libraries/wasi-nn/test/build/iwasm /run/iwasm
+
+ENTRYPOINT [ "/run/iwasm" ]