Created by: jeng1220

1. Add new search path for TensorRT at tensorrt.cmake. In NVIDIA official docker image, TensorRT headers are located at /usr/include/x86_64-linux-gnu and TensorRT libraries are located at /usr/lib/x86_64-linux-gnu, so using -DTENSORRT_ROOT will fail to detect TensorRT.

2. Add better debug message. There is no debug/warning message to tell developer that TensorRT is failed to be detected.

3. Fix the bug of detection of TensorRT version. In later version of TensorRT (e.g. v6), NV_TENSORRT_MAJOR is defined at NvInferVersion.h instead of NvInfer.h, so add compatibility fix.