Added real decode speed report to set it apart from the current output speed report in sample apps

[jeffqjiangNew]

• In sample apps, the current decode speed report is actually output/display speed report. This is all right for AVC and HEVC as decoded frames are normally displayed.
• Due to AV1's extensive use of alternative reference frames that are not displayed, AV1 decoded frame count and output/displayed frame count can be quite different, making the current speed report not an accurate decode speed measurement.
• We now added the actual decode speed report, besides the existing speed report, now called output/display FPS. This gives more accurate decode performance report for AV1.
• Made piccount the decoded frame count, in stead of the count for deocded frame wrap up previously.