FP16 Mode support

[PhuongNDVN]

Thank you for sharing this project. It's really helpful to me.

I tested examples without any issue with engine fp32. However, I'm getting issue with engine fp16. I can run normally but there no detection in the result. The engine with fp16, I built from yolov5 github with --half option. I think it comes from
DeviceMemory::setup() and CvCpuPreprocessor::process() because input should have type of 2 bytes, not 4 bytes

Updated: I updated the case when I succeeded and failed to get correct result. onnx is generated by yolov5-hub (fp16 generated by using --half option):

• onnx fp32 -> TensorRT fp32 (generated by yolov5-hub | this hub | nvidia container): success
• onnx (fp32) -> tensorrt fp16 (generated by this hub | nvidia container): success
• tensorrt fp16 (generated by yolov5-hub with --half option): failed
• onnx fp16 -> tensorrt fp16 (generated by this hub | nvidia container): failed

I think the issue for mode fp16 related to onnx-fp16. Please consider this issue when you have time. Thanks