audiounit: aggregate devices follow up (#247)
audiounit: aggregate devices follow up (#247)

* audiounit: signature refactor of set_aggregate_sub_device_list

* audiounit: signature refactor of destroy_aggregate_device

* audiounit: use AudioHardware Create/DestroyAggregateDevice API

* audiounit: address review comments

kinetiknz/cubeb,kinetiknz/cubeb,kinetiknz/cubeb