Optimization: Reduced decode session start latency for certain output surface memory types. (#512)

* *rocDecode/Optimization: Reduced decode session start latency for certain output surface memory types.

* * rocDecode/Optimization: Video decode RGB sample creates itsown HIP
  stream.

* * rocDecode/Optimization: Created separate HIP stream in each thread in
  video decode RGB sample.

* * rocDecode/Optimization: Addressed the lower FPS report in RGB sample:
  move HIP stream creation out of FPS calculation scope.

* * rocDecode/Optimize: Removed comments.

[ROCm/rocdecode commit: 1f53dedd4a]

projects/rocdecode/utils/rocvideodecode/roc_video_dec.cpp

@@ -1044,7 +1044,11 @@ bool RocVideoDecoder::InitHIP(int device_id) {
     }
     HIP_API_CALL(hipSetDevice(device_id));
     HIP_API_CALL(hipGetDeviceProperties(&hip_dev_prop_, device_id));
-    HIP_API_CALL(hipStreamCreate(&hip_stream_));
+    if (out_mem_type_ == OUT_SURFACE_MEM_DEV_INTERNAL || out_mem_type_ == OUT_SURFACE_MEM_NOT_MAPPED) {
+        hip_stream_ = 0; // Null stream. For internal device or unmapped memory, we don't need to create a hip stream.
+    } else {
+        HIP_API_CALL(hipStreamCreate(&hip_stream_));
+    }
     return true;
 }