force g711 test to match 1-channel sample data

special case the g711 test to know that it is a 1-channel input.
Test case itself can't infer the channel count from the g711 stream
since there is no header/control info within the g711 stream.

This is updated from the following commit in android10-tests-dev
https://android-review.googlesource.com/c/platform/frameworks/av/+/1138077
Instead of using component name, mime is used now to identify g711
decoder.

Bug: 140773833
Bug: 202600369

Test: atest VtsHalMediaC2V1_0TargetAudioDecTest
Change-Id: I88d60e0ea198c6f2c48899753f501e44961a090a