Rr/ffmpeg sw decoder (#480)

* WIP: ffmpeg based software decoder

* minor update

* WIP: FFMpeg SW decoder support

* FFMpeg decoder working version

* working version without threading

* multithreading working with FFMpeg decoder

* moved ffmpeg decoder to separate folder

* updated changelog

* minor change

* resolved review comments

* resolved review comments

* fixed a bug in hipMemcpy for copying decoded output to GPU

* added support for multithreading in FFMpeg decoder

* addressed review comments

* fixed format changes requested

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Co-authored-by: Lakshmi Kumar <lakshmi.kumar@amd.com>

[ROCm/rocdecode commit: 5365ceabec]

projects/rocdecode/utils/ffmpegvideodecode/ffmpeg_video_dec.h

@@ -174,6 +174,7 @@ class FFMpegVideoDecoder: public RocVideoDecoder {
         void DecodeThread();
         int DecodeAvFrame(AVPacket *av_pkt, AVFrame *p_frame);
         void InitOutputFrameInfo(AVFrame *p_frame);
+        int FlushDecoder();
         void PushPacket(AVPacket *pkt) {
             {
                 std::lock_guard<std::mutex> lock(mtx_pkt_q_);