Audio encoder specifies channel-range

Allow the audio encoder XML to specify ranges of channels instead
of just a max (which had implied min==1).

Bug: 156273760
Test: atest android.media.cts.MediaCodecTest#testPrependHeadersToSyncFrames
Change-Id: Ib862e09074ffc34874f2c7d1a9f074096cebc046
Merged-In: Ib862e09074ffc34874f2c7d1a9f074096cebc046