With the introducation of the Audio_in session interface it makes
sense to rename the current available audio drivers. At the moment
only the dde_bsd audio_drv supports Audio_out as well as Audio_in.
The Linux audio_drv only supports Audio_out (there is no demand for
Audio_in support currently) but is renamed nonetheless to make it
easiert to write generic run scripts.
Issue #1644.
This patch changes the top-level directory layout as a preparatory
step for improving the tools for managing 3rd-party source codes.
The rationale is described in the issue referenced below.
Issue #1082