make opus encoder test follow CDD

change sample rates and channel counts for opus encoder match what is
documented in the CDD. link the test to the appropriate CDD section.

Bug: 170689476
Test: atest android.media.cts.EncoderTest#testOpusEncoders
Change-Id: I00af7597e4e81203bbde9396d8de8b42d6a1d25a
1 file changed