codecs: Enable codec unit tests in postsubmit

Enabled unit tests for mp3, mpeg4, h263, flac and amr codecs in
postsubmit.

Most of these were marked as dynamic-presubmit and those are now
changed to postsubmit as these tests now use DynamicConfig.xml and
can download the required files without any extra arguments.
After some time of running these in postsubmit, these will be changed
to presubmit.

- For AMR wb, TEST_MAPPING was present only in encoder. That is now
  moved and updated to include both encoder and decoder tests to be
  consistent with AMR nb.
- Added TEST_MAPPING for flac decoder wrapper
- Added FlacDecoderTest to device-tests

Bug: 304383609
Test: atest-dev Mp3DecoderTest Mpeg4H263EncoderTest \
 Mpeg4H263DecoderTest AmrwbDecoderTest AmrwbEncoderTest \
 AmrnbEncoderTest AmrnbDecoderTest FlacDecoderTest

Change-Id: I3b549236e4857952eadffb25009f33056eadbf41