VTS: Refactor Video and Audio decoder test functions

Move info file handling and Audio Decoder's timestamp
validation to a function

Bug: 154736583
Test: atest VtsHalMediaC2V1_0TargetAudioDecTest \
  VtsHalMediaC2V1_0TargetVideoDecTest

Change-Id: Iead1be0228896b10d92d49ea27a9692d0745046b
5 files changed