Perf sample: Added decoded frame number and display delay options to video decode performance sample. (#405)

* * rocDecode/Perf sample: Added decoded frame number and display delay options to video decode performance sample. Also changed default thread number from 4 to 1.

* * rocDecode: Added max number of decoded frames option to decode sample script. This is useful to do partial decoding test on long streams.

* * rocDecode: Updated README.md.

* * rocDecode: Minor correction.

[ROCm/rocdecode commit: c486a7f6b4]

projects/rocdecode/samples/videoDecodePerf/README.md

@@ -30,7 +30,9 @@ make -j
 
 ```shell
 ./videodecodeperf -i <input video file [required]> 
-                  -t <number of threads [optional - default:4]>
+                  -t <number of threads [optional - default:1]>
+                  -f <Number of decoded frames - specify the number of pictures to be decoded [optional]>
+                  -disp_delay <display delay - specify the number of frames to be delayed for display [optional]>
                   -d <Device ID (>= 0) [optional - default:0]>
                   -z <force_zero_latency - Decoded frames will be flushed out for display immediately [optional]>
 ```