Rename the old audio HAL to 'legacy'

Move the HAL for the audio forwarder out of the way. This uses the vsoc
kernel interface which we are deprecating in favor of VMM support for
audio. No functional difference in built components.

Bug: 126955561
Test: local build, stream_audio was still working
Change-Id: I00a9b97208d16942528a6853665ff1b4d87e1d2e