AudioSystem: update framework channel capabilities

Anticipate more than 8 channels (such as 7.1.4) on
future devices, but keep at 8 for now.

Test: atest AudioTrackTest#testImmersiveStreaming
Test: same test by manually adjusting to 24 channels.
Bug: 127896072
Bug: 187062102
Change-Id: I72c2ff0faa7794f22deaeb794920afb65788f40b